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000-833 Object Oriented Analysis and Design - Part 1 (Analysis)

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000-833 exam Dumps Source : Object Oriented Analysis and Design - Part 1 (Analysis)

Test Code : 000-833
Test Name : Object Oriented Analysis and Design - Part 1 (Analysis)
Vendor Name : IBM
Q&A : 50 Real Questions

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IBM Object Oriented Analysis and

Object-Oriented analysis and Design | killexams.com Real Questions and Pass4sure dumps

This chapter is from the publication 

analysis emphasizes an investigation of the issue and requirements, in place of a solution. as an example, if a brand new on-line trading device is desired, how will it's used? What are its functions?

"evaluation" is a vast term, most useful qualified, as in necessities evaluation (an investigation of the requirements) or object-oriented analysis (an investigation of the domain objects).

Design emphasizes a conceptual solution (in application and hardware) that fulfills the necessities, in preference to its implementation. as an example, a description of a database schema and utility objects. Design concepts regularly exclude low-level or "obvious" details—obvious to the meant consumers. eventually, designs will also be carried out, and the implementation (similar to code) expresses the genuine and comprehensive realized design.

As with evaluation, the term is superior certified, as in object-oriented design or database design.

positive evaluation and design were summarized in the phrase do the correct element (evaluation), and do the element correct (design).

Object-Oriented evaluation And Design — Introduction (part 1) | killexams.com Real Questions and Pass4sure dumps

The thought Of Object-Orientation

Object-orientation is what’s known as a programming paradigm. It’s not a language itself but a set of concepts it really is supported by means of many languages.

in case you aren’t standard with the ideas of object-orientation, you may additionally take a look on the Story of Object-Oriented Programming.

If every little thing we do in these languages is object-oriented, it ability, we're oriented or focused around objects.

Now in an object-oriented language, this one enormous program will as an alternative be cut up apart into self contained objects, nearly like having a couple of mini-courses, each object representing a special a part of the utility.

and each object incorporates its own information and its own good judgment, and that they speak between themselves.

These objects aren’t random. They symbolize the manner you talk and feel about the difficulty you are trying to remedy to your actual existence.

They characterize things like personnel, photographs, financial institution money owed, spaceships, asteroids, video segment, audio data, or something exists to your software.

Object-Oriented analysis And Design (OOAD)

It’s a structured formula for examining, designing a system by using applying the item-oriented ideas, and boost a group of graphical gadget models all through the building lifestyles cycle of the application.

OOAD in the SDLC

The software lifestyles cycle is usually divided up into tiers going from abstract descriptions of the problem to designs then to code and trying out and finally to deployment.

The earliest stages of this process are analysis (requirements) and design.

The difference between evaluation and design is commonly described as “what Vs how”.

In analysis developers work with users and area experts to outline what the system is meant to do. Implementation details are presupposed to be normally or absolutely disregarded at this phase.

The goal of the analysis part is to create a model of the system inspite of constraints reminiscent of appropriate know-how. here's usually executed by means of use circumstances and abstract definition of essentially the most crucial objects the use of conceptual model.

The design part refines the evaluation model and applies the obligatory know-how and different implementation constrains.

It specializes in describing the objects, their attributes, habits, and interactions. The design model should have the entire details required in order that programmers can enforce the design in code.

They’re optimal performed in an iterative and incremental utility methodologies. So, the activities of OOAD and the developed models aren’t executed once, we are able to revisit and refine these steps constantly.

Object-Oriented evaluation

within the object-oriented analysis, we …

Elicit necessities: define what does the utility should do, and what’s the difficulty the software making an attempt to clear up.

Specify requirements: Describe the requirements, usually, using use circumstances (and scenarios) or user experiences.

Conceptual mannequin: establish the critical objects, refine them, and define their relationships and behavior and draw them in an easy diagram.

We’re not going to cover the first two actions, just the final one. These are already explained in element in necessities Engineering.

Object-Oriented Design

The analysis phase identifies the objects, their relationship, and behavior the usage of the conceptual model (an abstract definition for the objects).

while in design part, we describe these objects (with the aid of creating class diagram from conceptual diagram — always mapping conceptual mannequin to category diagram), their attributes, behavior, and interactions.

in addition to applying the software design principles and patterns which could be lined in later tutorials.

The enter for object-oriented design is equipped through the output of object-oriented evaluation. however, analysis and design may happen in parallel, and the consequences of 1 activity will also be used by using the different.

within the object-oriented design, we …

Describe the classes and their relationships the usage of classification diagram.

Describe the interplay between the objects the use of sequence diagram.

observe application design ideas and design patterns.

a category diagram offers a visual illustration of the classes you want. And here is the place you get to be definitely certain about object-oriented principles like inheritance and polymorphism.

Describing the interactions between these objects allows you to improved remember the responsibilities of the diverse objects, the behaviors they deserve to have.

— different diagrams

there are many different diagrams we will use to model the system from distinctive perspectives; interactions between objects, constitution of the system, or the behavior of the gadget and the way it responds to hobbies.

It’s all the time about choosing the right diagram for the right want. make sure to understand which diagrams could be advantageous when considering or discussing a condition that isn’t clear.

equipment modeling and the distinct models we are able to use will be discussed subsequent.

system Modeling

gadget modeling is the procedure of developing models of the equipment, with every mannequin representing a different views of that equipment.

probably the most essential point about a system mannequin is that it leaves out aspect; It’s an abstract representation of the system.

The models are usually in accordance with graphical notation, which is almost always according to the notations within the Unified Modeling Language (UML). different models of the gadget like mathematical model; a detailed system description.

models are used all over the analysis process to support to elicit the necessities, right through the design manner to explain the gadget to engineers, and after implementation to doc the device constitution and operation.

different views

We may increase a model to signify the gadget from different views.

exterior, the place you model the context or the atmosphere of the system.

interaction, where you mannequin the interplay between components of a device, or between a system and other programs.

Structural, where you model the organization of the system, or the structure of the data being processed by the system.

Behavioral, where you model the dynamic habits of the gadget and how it respond to routine.

Unified Modeling Language (UML)

The unified modeling language become the average modeling language for object-oriented modeling. It has many diagrams, besides the fact that children, essentially the most diagrams which are conventional are:

Use case diagram: It suggests the interplay between a equipment and it’s ambiance (clients or techniques) within a particular condition.

classification diagram: It suggests the diverse objects, their relationship, their behaviors, and attributes.

Sequence diagram: It indicates the interactions between the distinctive objects within the system, and between actors and the objects in a device.

State computing device diagram: It indicates how the system respond to exterior and inner events.

recreation diagram: It indicates the move of the statistics between the methods within the gadget.

that you could do diagramming work on paper or on a whiteboard, at the least within the initial degrees of a task. however there are some diagramming tools as a way to support you to attract these UML diagrams.

record: IBM Outpaces opponents in utility construction application marketplace for Seventh Straight year | killexams.com Real Questions and Pass4sure dumps

source: IBM

June 13, 2008 08:00 ET

ARMONK, ny--(Marketwire - June 13, 2008) - IBM (NYSE: IBM) nowadays introduced that analyst firm Gartner, Inc.* and market analysis enterprise Evans statistics Corp. have ranked IBM as the chief within the application building application market. These rankings come just as IBM is projecting greater than 12,000 people will attend its 2008 IBM Rational application development Conferences in 13 international locations worldwide.

Gartner named IBM the global market share leader in application development in accordance with complete utility salary in 2007 and Evans information Corp. survey respondents who were users of IBM Rational utility Developer ranked it the number 1 integrated Developer ambiance (IDE) for user satisfaction. this is the seventh consecutive 12 months that Gartner has ranked IBM the chief and 2nd consecutive 12 months that IBM Rational application Developer changed into chosen as the Developer's option appropriate IDE by way of the 1,200 builders international taking part in the survey.

in line with the independent Gartner record, IBM is the main market share vendor in total software earnings, with 37.eight percent market share -- superior market share than its three closest opponents combined. The worldwide application building application market grew greater than 10% percent in 2007 to very nearly $6.9 billion, in accordance with Gartner.

IBM became also mentioned for its typical leadership in accordance with total utility salary for 2007 across software construction market sub-categories, together with SCCM disbursed, Object Oriented analysis & Design and Java Platform ad tool. Telelogic, currently bought by way of IBM, had a 2007 marketshare of forty.6 % within the requirements Elicitation and management category in line with complete software earnings.

"With the upward push of globally dispensed software development teams, consumers are searching for skilled providers to help them collaborate in an open and transparent manner," mentioned Dr. Daniel Sabbah, common supervisor, IBM Rational software. "We agree with the powerful response from the Evans information and Gartner experiences coincides with the remarks we've got bought from consumers about IBM's approach round advantageous application birth."

IBM Kicks off the world's Most Attended Developer convention sequence

This marketshare information coincides with IBM's announcement that over 12,000 members are anticipated to attend the 15 IBM Rational application construction Conferences deliberate around the globe. Following the event held last week in Orlando, FL, IBM will take the display on the highway to 17 cities including Sharm El Sheikh, Egypt; San Paulo, Brazil; Bangalore, India; Shanghai, China; Rome and Milan, Italy.

For convention attendees using an iPhone, IBM is releasing a conference scheduler written in commercial enterprise technology Language (EGL) to enable iPhone clients to dynamically journey the IBM Rational utility building conference via an interface that they feel at ease with. using internet 2.0 and social engineering ideas, users can deliver remarks on and chat about sessions, navigate the convention looking for tracks and movements, and use artistic expertise that suggests which talks the person should attend next in keeping with preferences.

on the annual IBM Rational application building convention in Orlando, Florida, greater than 3,500 attendees realized about new software and courses that aid valued clientele seriously change how they're birth application on a global scale. The announcement of recent products, services and company associate initiatives are designed to transform how IBM Rational utility can assist customers force superior price and performance from their globally allotted application investments.

shoppers unable to attend the conference in the community can view the keynote presentations on IBM tv.

IBM helps developers stay aggressive in trendy quick-paced development ambiance. imaginative classes similar to IBM developerWorks, the premier technical useful resource for application developers, and IBM alphaWorks, IBM's rising applied sciences outlet, give an online group for the builders of today and day after today. developers who're unbiased utility vendors can take competencies of income and marketing equipment, ability-building lessons and technical aid with the aid of becoming a member of the international IBM PartnerWorld software. IBM's tutorial Initiative and IBM Rational application building convention are examples of the continuing researching and neighborhood-constructing courses needed by students, educators and developers international.

For greater suggestions, consult with http://www.ibm.com/software/rational.

*"Market Share: utility building software, international, 2007" by way of Laurie Wurster, Teresa Jones and Asheesh Raina, may additionally 2008.

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Object Oriented Analysis and Design - Part 1 (Analysis)

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Object-Oriented Analysis And Design — Introduction (Part 1) | killexams.com real questions and Pass4sure dumps

The Concept Of Object-Orientation

Object-orientation is what’s referred to as a programming paradigm. It’s not a language itself but a set of concepts that is supported by many languages.

If you aren’t familiar with the concepts of object-orientation, you may take a look at The Story of Object-Oriented Programming.

If everything we do in these languages is object-oriented, it means, we are oriented or focused around objects.

Now in an object-oriented language, this one large program will instead be split apart into self contained objects, almost like having several mini-programs, each object representing a different part of the application.

And each object contains its own data and its own logic, and they communicate between themselves.

These objects aren’t random. They represent the way you talk and think about the problem you are trying to solve in your real life.

They represent things like employees, images, bank accounts, spaceships, asteroids, video segment, audio files, or whatever exists in your program.

Object-Oriented Analysis And Design (OOAD)

It’s a structured method for analyzing, designing a system by applying the object-orientated concepts, and develop a set of graphical system models during the development life cycle of the software.

OOAD In The SDLC

The software life cycle is typically divided up into stages going from abstract descriptions of the problem to designs then to code and testing and finally to deployment.

The earliest stages of this process are analysis (requirements) and design.

The distinction between analysis and design is often described as “what Vs how”.

In analysis developers work with users and domain experts to define what the system is supposed to do. Implementation details are supposed to be mostly or totally ignored at this phase.

The goal of the analysis phase is to create a model of the system regardless of constraints such as appropriate technology. This is typically done via use cases and abstract definition of the most important objects using conceptual model.

The design phase refines the analysis model and applies the needed technology and other implementation constrains.

It focuses on describing the objects, their attributes, behavior, and interactions. The design model should have all the details required so that programmers can implement the design in code.

They’re best conducted in an iterative and incremental software methodologies. So, the activities of OOAD and the developed models aren’t done once, we will revisit and refine these steps continually.

Object-Oriented Analysis

In the object-oriented analysis, we …

Elicit requirements: Define what does the software need to do, and what’s the problem the software trying to solve.

Specify requirements: Describe the requirements, usually, using use cases (and scenarios) or user stories.

Conceptual model: Identify the important objects, refine them, and define their relationships and behavior and draw them in a simple diagram.

We’re not going to cover the first two activities, just the last one. These are already explained in detail in Requirements Engineering.

Object-Oriented Design

The analysis phase identifies the objects, their relationship, and behavior using the conceptual model (an abstract definition for the objects).

While in design phase, we describe these objects (by creating class diagram from conceptual diagram — usually mapping conceptual model to class diagram), their attributes, behavior, and interactions.

In addition to applying the software design principles and patterns which will be covered in later tutorials.

The input for object-oriented design is provided by the output of object-oriented analysis. But, analysis and design may occur in parallel, and the results of one activity can be used by the other.

In the object-oriented design, we …

Describe the classes and their relationships using class diagram.

Describe the interaction between the objects using sequence diagram.

Apply software design principles and design patterns.

A class diagram gives a visual representation of the classes you need. And here is where you get to be really specific about object-oriented principles like inheritance and polymorphism.

Describing the interactions between those objects lets you better understand the responsibilities of the different objects, the behaviors they need to have.

— Other diagrams

There are many other diagrams we can use to model the system from different perspectives; interactions between objects, structure of the system, or the behavior of the system and how it responds to events.

It’s always about selecting the right diagram for the right need. You should realize which diagrams will be useful when thinking about or discussing a situation that isn’t clear.

System modeling and the different models we can use will be discussed next.

System Modeling

System modeling is the process of developing models of the system, with each model representing a different perspectives of that system.

The most important aspect about a system model is that it leaves out detail; It’s an abstract representation of the system.

The models are usually based on graphical notation, which is almost always based on the notations in the Unified Modeling Language (UML). Other models of the system like mathematical model; a detailed system description.

Models are used during the analysis process to help to elicit the requirements, during the design process to describe the system to engineers, and after implementation to document the system structure and operation.

Different Perspectives

We may develop a model to represent the system from different perspectives.

External, where you model the context or the environment of the system.

Interaction, where you model the interaction between components of a system, or between a system and other systems.

Structural, where you model the organization of the system, or the structure of the data being processed by the system.

Behavioral, where you model the dynamic behavior of the system and how it respond to events.

Unified Modeling Language (UML)

The unified modeling language become the standard modeling language for object-oriented modeling. It has many diagrams, however, the most diagrams that are commonly used are:

Use case diagram: It shows the interaction between a system and it’s environment (users or systems) within a particular situation.

Class diagram: It shows the different objects, their relationship, their behaviors, and attributes.

Sequence diagram: It shows the interactions between the different objects in the system, and between actors and the objects in a system.

State machine diagram: It shows how the system respond to external and internal events.

Activity diagram: It shows the flow of the data between the processes in the system.

You can do diagramming work on paper or on a whiteboard, at least in the initial stages of a project. But there are some diagramming tools that will help you to draw these UML diagrams.

MET CS 770 Object-Oriented Analysis & Design | killexams.com real questions and Pass4sure dumps

Last updated: November 13, 2002 Recent updates are often in red.

Contacting Eric Braude changed if this is red Materials changed if this is red Forums changed if this is red Overview changed if this is red Grading changed if this is red Project Organization changed if this is red Homework and Due Dates changed if this is red Phase 3 Required Background changed if this is red Learning Objectives changed if this is red Syllabus and Dates for Classes changed if this is red Overview

A major engineering problem today is the predictable development of reliable software-intensive systems. The object-oriented paradigm is an important part of such development.

Object-oriented methods can be divided into languages, distribution, and analysis and design. There change in the language category, particularly Java and C#. Distribution includes the use of vendor libraries of classes and also distributed objects as specified by the Object Management Group etc. Basic to the entire enterprise, however, are analysis and design, which has remained remarkable stable for years. Object-Oriented Analysis and Design includes the overall goals of the object paradigm, the selection of classes, the relationships among them, and their utilization to implement systems.

Required Background

A knowledge of C++ or Java (MET CS 565) and software engineering methods (MET CS 673) are required. It is preferable to have taken Design Patterns (MET CS 665).

Materials and references

The recommended textbook is “Applying UML and Patterns: An Introduction to Object-Oriented Analysis and Design, and the Unified Process ” by Larman (Prentice Hall) 2nd edition, Published July 2001, 627 pages, ISBN 0130925691. This is the first time that this instructor has used this book, and it is not clear how much the book will be used.

The instructor will provide notes for all classes.

Other references:

The Unified Modeling Language User Guide by Booch et al (Prentice Hall) ISBN0-201-57168-4

The Unified Modeling Language Reference Manual James Rumbaugh, Ivar Jacobson, Grady Booch Addison-Wesley Pub Co; ISBN: 020130998X

Design Patterns by Gamma et al

Object-Oriented Software Engineering by I Jacobson

Object-Oriented Analysis & Design by G. Booch

Modeling the world in data by S. Schlaer and S. Mellor

Modeling the world in states by S. Schlaer and S. Mellor

The Unified Method draft www.rational.com

Object-oriented Analysis by P. Coad and E. Yourdon

Object-oriented Design by P. Coad and E. Yourdon

Object-oriented Programming by P. Coad and A Nicola

Software Engineering: An Object-Oriented Perspective by Eric Braude

Learning Objectives

Students will be able to …

… analyze problems from an object perspective

… create OO designs which are ready for coding

… implement a pilot OO project

Grading

The course will consist of homework and a project, weighted as follows:

1. Homework: 30%

2. Project: 70%

There are three phases for the project, graded as follows:

phase 1 (problem statement): 1/9

phase 2 (analysis): 2/9

phase 3 (design): 1/3

phase 4 (implementation and critical review): 1/3

Parts are evaluated equally unless otherwise stated.

Late homework is not accepted unless there is a reason why it was impossible for you. If there is such an impossibility, the work will be graded on a pass/fail basis.

Project Organization

You will be required to submit an analyzed, designed and implemented project according to the deadlines shown in the schedule. Detailed requirements will follow.

With the instructor’s permission, it may be possible to substitute all or part of the project with an investigation of tools for OOA&D such as Rational Rose or Together. This will require a detailed evaluation and an investigation of how these tools are being used extensively in a particular company.

Teams two are permitted, and will be evaluated at a higher standard. All members must know all parts.

You will be required to give a presentation on at least two of the phases in your project.

Syllabus:

This syllabus is subject to about 15% modification.

The order of topics will be driven by the notes, which the instructor will hand out, not by the textbook. The textbook will serve as background and reference.

Wk. Date Topic Text

chapters

Project

Times are approximate. See “date homework due” section for final dates

1 9/3

Review Syllabus

Review Software Development Process

Notes 0-1 Phase 1 assigned 2 9/10

Introduction, Overview, and Goals of Design

UML as required

Extreme programming and refactoring

Notes 1-3 3 9/17

Requirements I: Use Cases

Notes 13 part 1 Presentations;

Assign phase 2

4 9/24

Requirements II: Sequence Diagrams

Notes 13 part 2 Phase 1 due; 5 10/1

Requirements III: Completing Domain Classes

Writing Detailed Requirements

Review Student Designs

Notes 13 part 3

Larman 10

6 10/8 Notes 14 part 1 Assign phase 3 7 10/22 To be determined Presentations; Phase 2 due; 8 10/29

Review Design Patterns as required

Discussion of Tools

Review Student Designs

Notes 4-6 9 11/5

Frameworks

Review Student Designs

Presentations on architectures 10 11/12

Design Topics

Review Student Designs

Notes 14 part 2 Assign phase 4

Phase 3 due

11 11/19 Presentations on detailed designs 12 11/26

Detailed Design

Review Student Designs

Presentations 13 12/3

Implementing OO designs

Shlaer-Mellor

Presentation of results (1 of 2) 14 12/10

Presentations on Finished Applications

Phase 4 due Presentation of results (2 of 2)

Notes are from Software Design (Braude, to be published by Wiley in March 2002)

** Applying UML and Patterns: … (Larman)

Dates Homework is due

Num-ber Name Due date Project phase 1 9/24 1 “Design Issues” 9/17 1 3.4 (Pass Fail) 9/17 Project phase 2: (10/2/2002

)

1.Attach first a copy of your phase 1. Respond specifically to whatever comments I may have made on your phase 1. You can write these directly on the copy.

Show the sequence diagrams for at least the two use cases you have introduced. Key them to the use case steps, which you should number.3.List requirements by “domain class” paragraphs, including

— The testable functionality that the application will definitely accomplish

–What you would like to have the application accomplish if time permits

Criterion: a. Requirements clearly written. (A = very clear description of application’s goals; no detail omitted)

4.Provide a class diagram for your project consisting of all of the domain classes as well as the domain packages that you will use.

Criteria:

b. Clarity and completeness Sufficiency of key classes for committed requirements and use cases (A = very clear class meanings; no domain class missing no other domain classes required)

g. Economy (A = no redundancy at all in the class model)

Here are some typical improvements.

Most room for improvement

1. Make your domain names specific to your application; e.g., PetStoreTransaction, FootballGame, FootballTeam rather than Transaction or Game or Team.

2. Use the “entities” section correctly. This applies when there are specific entities that the application is required to have. It does not include entities that will be created at runtime that you can’t specify entirely at requirements time.

3. Many internal classes have corresponding GUI classes. For example, PetStoreAccount entities may get their data from a PetStoreAccountGUI entity. Specify the latter in its own category rather than under PetStoreAccount.

4. In your requirements, distinguish between the initiator and the substance of functionality.

For example, under “Courses” a functionality might be “12.1.5 The application shall be able to display the catalog description of each course in the following format …” (Corresponds to class Course). Under the “Course GUI” paragraph an event might be “When the display course button is pressed, the functionality described in section 12.1.5 is initated.” Under the “Student GUI” paragraph an event might be “When the show course button is pressed, the functionality described in section 12.1.5 is initated.” Etc.

Do not say “12.1.5 When the display course button is pressed on the Course GUI, the application can display the catalog description of each course in the following format …” Otherwise you will have a maintenance nightmare and a poor mapping to the design and implementation.

Room for improvement

1. Most

objects are not sensitive to events unless they are GUI objects. Buttons are examples. Many objects have functionality that may be invoked as a result of an event on an

other object. For example, a customer’s information may be displayed when the button is clicked. But “display” is a function of Customer: Any one of clients can invoke it, some event-sensitive and others not. The object with (direct) event reaction is the button, not the customer.

2. In your requirements document, don’t say “The customer shall include a name …” (which is strange English). Instead: “The application shall maintain the name of customers ….”

3. Distinguish between objects and object aggregates. For example, you could have a “Customers” requirements paragraph with functionality such as “App shall be able to send a customer profile to the central database.” This will correspond to a class Customer. You could also have a “Customer List” paragraph with functionality such as “It shall be possible to add new customers …” This will correspond to a class such as CustomerList.

4. Don’t waste words. In particular, give a sentence or two under each paragraph that adds value.

NOT:

1.4 Customers

This section describes the requirements for customers.

BUT

1.4 Customers

The application shall track the customers of the video store as follows. …

10/22 3 Clown problem 10/9/02

Draw a class model for an application for drawing human figures. The picture shown is a typical product of the application. The figures are always neck-upward; mouths are always lines, necks always rectangles, etc. – the shapes that appear in the figure. Assume that the business will never change — but we want to be able to easily upgrade the shop’s capability within these constraints (e.g., draw necks with various colors, new kinds of border lines). The class model should make figure drawing convenient (e.g., allowing the retrieval of previously constructed figure parts). Show attributes or operations whenever they clarify your solution. Include useful abstractions (but to extend the current business).

There is no requirement to take into account the GUI for the application (icons, menu’s etc.)

Here is a scenario:

The user … pulls onto the monitor “abeLincolnFace14” (which excludes the ears and neck)

… adds “ear123” on the left by dragging to its vicinity and releasing

The application places ear123 in a correct position

The user invokes the “complete with suitable parts” command.

The application

… completes the figure with a neck and hat that it considers most suitable.

… creates an ear on the right, complete with matching position, interior texture and color, and styles of border lines

Criteria: a. completeness relative to requirements (A = sufficient classes for requirements, including appropriate generalizations)

b. economy of classes (A = no more than necessary for requirements)

10/29 4 14.1 – 14.6 11/5 see more below see below

Project Phase 3: Due 11/12

1. Attach a copy of your phase 2 as graded by me, with specific responses to whatever comments I may have made on your phase 2.

2. Provide a class diagram for your project, showing inheritance and aggregation. Show key methods, key dependencies, and inheritance and aggregation. Use your packages and Facades to avoid a single overwhelming figure.

3. Show at least one additional model that completes your design.

Criteria:

a. Clarity of the model (A = very clear class meanings; very clear organization; no unnecessary details)

b. Adequacy of class model for effecting the requirements. (A= detailed enough to clearly allow an implementation that satisfies the requirements.)

g. Completeness **** of models to specify the entire design. (A=right models selected; clearly no gaps in description)

Most room for improvement

1. If you use a data flow diagram, indicate the data types that flow.

2. If you use a data flow diagram, indicate the functionality at each processing node.

3. In the interest of clarity, show the relationships among the packages. You can employ <<uses>> relationships. Omit the classes from such a figure.

Room for improvement

1. In this course we did not give meaning to solid lines with arrows. Explain what you mean by them, or don’t use them.

2. Be specific about associations: Do you mean two-way aggregations?

3. You have introduced a class whose name does not indicate a clear purpose and which is not a domain class. Explain it’s purpose.

A Little room for improvement

1. …..

Project Phase 4: Due 12/10

Section 1 Attach Phases 2 and 3. Response to my comments on phase 3. ( not graded, but required)

Section 2 Show representative input and output.

Section 3 Explain the application of all of the steps covered in the notes — explain if they did not apply.

(criterion: a. Clarity and completeness — A = all relevant steps thoroughly implemented where applicable and explained where not)

Section 4 Provide a complete class diagram and other appropriate model(s), building on the models you submitted for phase 3.

(criterion: b. clarity and completeness — A = very clearly chosen and arranged models)

Section 5 Account of the degree to which you accomplished your requirements as given in phase 2. Please refer to them by number (e.g., 11.3.5).

(criterion: g. degree of accomplishment. A = excellent functional capabilities for a graduate course)

Section 6. Source code.

(d. criterion: clarity — A = extremely clear layout & code; each part easily traceable to the corresponding design element)

Please …

note that your class diagrams and code must be consistent;

indicate all differences with prior design decisions;

indicate all sections using numbered tabs (e.g., Post-it notes)

Forums — past and present

Fall 2001

Fall 2002 email to the group is: 770F02@yahoogroups.com

Object-oriented design patterns in the kernel, part 2 | killexams.com real questions and Pass4sure dumps

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June 7, 2011

This article was contributed by Neil Brown

In the first part of this analysis we looked at how the polymorphic side of object-oriented programming was implemented in the Linux kernel using regular C constructs. In particular we examined method dispatch, looked at the different forms that vtables could take, and the circumstances where separate vtables were eschewed in preference for storing function pointers directly in objects. In this conclusion we will explore a second important aspect of object-oriented programming - inheritance, and in particular data inheritance.

Data inheritance

Inheritance is a core concept of object-oriented programming, though it comes in many forms, whether prototype inheritance, mixin inheritance, subtype inheritance, interface inheritance etc., some of which overlap. The form that is of interest when exploring the Linux kernel is most like subtype inheritance, where a concrete or "final" type inherits some data fields from a "virtual" parent type. We will call this "data inheritance" to emphasize the fact that it is the data rather than the behavior that is being inherited.

Put another way, a number of different implementations of a particular interface share, and separately extend, a common data structure. They can be said to inherit from that data structure. There are three different approaches to this sharing and extending that can be found in the Linux kernel, and all can be seen by exploring the struct inode structure and its history, though they are widely used elsewhere.

Extension through unions

The first approach, which is probably the most obvious but also the least flexible, is to declare a union as one element of the common structure and, for each implementation, to declare an entry in that union with extra fields that the particular implementation needs. This approach was introduced to struct inode in Linux-0.97.2 (August 1992) when

union { struct minix_inode_info minix_i; struct ext_inode_info ext_i; struct msdos_inode_info msdos_i; } u;

was added to struct inode. Each of these structures remained empty until 0.97.5 when i_data was moved from struct inode to struct ext_inode_info. Over the years several more "inode_info" fields were added for different filesystems, peaking at 28 different "inode_info" structures in 2.4.14.2 when ext3 was added.

This approach to data inheritance is simple and straightforward, but is also somewhat clumsy. There are two obvious problems. Firstly, every new filesystem implementation needs to add an extra field to the union "u". With 3 fields this may not seem like a problem, with 28 it was well past "ugly". Requiring every filesystem to update this one structure is a barrier to adding filesystems that is unnecessary. Secondly, every inode allocated will be the same size and will be large enough to store the data for any filesystem. So a filesystem that wants lots of space in its "inode_info" structure will impose that space cost on every other filesystem.

The first of these issues is not an impenetrable barrier as we will see shortly. The second is a real problem and the general ugliness of the design encouraged change. Early in the 2.5 development series this change began; it was completed by 2.5.7 when there were no "inode_info" structures left in union u (though the union itself remained until 2.6.19).

Embedded structures

The change that happened to inodes in early 2.5 was effectively an inversion. The change which removed ext3_i from struct inode.u also added a struct inode, called vfs_inode, to struct ext3_inode_info. So instead of the private structure being embedded in the common data structure, the common data structure is now embedded in the private one. This neatly avoids the two problems with unions; now each filesystem needs to only allocate memory to store its own structure without any need to know anything about what other filesystems might need. Of course nothing ever comes for free and this change brought with it other issues that needed to be solved, but the solutions were not costly.

The first difficulty is the fact that when the common filesystem code - the VFS layer - calls into a specific filesystem it passes a pointer to the common data structure, the struct inode. Using this pointer, the filesystem needs to find a pointer to its own private data structure. An obvious approach is to always place the struct inode at the top of the private inode structure and simply cast a pointer to one into a pointer to the other. While this can work, it lacks any semblance of type safety and makes it harder to arrange fields in the inode to get optimal performance - as some kernel developers are wont to do.

The solution was to use the list_entry() macro to perform the necessary pointer arithmetic, subtracting from the address of the struct inode its offset in the private data structure and then casting this appropriately. The macro for this was called list_entry() simply because the "list.h lists" implementation was the first to use this pattern of data structure embedding. The list_entry() macro did exactly what was needed and so it was used despite the strange name. This practice lasted until 2.5.28 when a new container_of() macro was added which implemented the same functionality as list_entry(), though with slightly more type safety and a more meaningful name. With container_of() it is a simple matter to map from an embedded data structure to the structure in which it is embedded.

The second difficulty was that the filesystem had to be responsible for allocating the inode - it could no longer be allocated by common code as the common code did not have enough information to allocate the correct amount of space. This simply involved adding alloc_inode() and destroy_inode() methods to the super_operations structure and calling them as appropriate.

Void pointers

As noted earlier, the union pattern was not an impenetrable barrier to adding new filesystems independently. This is because the union u had one more field that was not an "inode_info" structure. A generic pointer field called generic_ip was added in Linux-1.0.5, but it was not used until 1.3.7. Any file system that does not own a structure in struct inode itself could define and allocate a separate structure and link it to the inode through u.generic_ip. This approach addressed both of the problems with unions as no changes are needed to shared declarations and each filesystem only uses the space that it needs. However it again introduced new problems of its own.

Using generic_ip, each filesystem required two allocations for each inode instead of one and this could lead to more wastage depending on how the structure size was rounded up for allocation; it also required writing more error-handling code. Also there was memory used for the generic_ip pointer and often for a back pointer from the private structure to the common struct inode. Both of these are wasted space compared with the union approach or the embedding approach.

Worse than this though, an extra memory dereference was needed to access the private structure from the common structure; such dereferences are best avoided. Filesystem code will often need to access both the common and the private structures. This either requires lots of extra memory dereferences, or it requires holding the address of the private structure in a register which increases register pressure. It was largely these concerns that stopped struct inode from ever migrating to broad use of the generic_ip pointer. It was certainly used, but not by the major, high-performance filesystems.

Though this pattern has problems it is still in wide use. struct super_block has an s_fs_info pointer which serves the same purpose as u.generic_ip (which has since been renamed to i_private when the u union was finally removed - why it was not completely removed is left as an exercise for the reader). This is the only way to store filesystem-private data in a super_block. A simple search in the Linux include files shows quite a collection of fields which are void pointers named "private" or something similar. Many of these are examples of the pattern of extending a data type by using a pointer to a private extension, and most of these could be converted to using the embedded-structure pattern.

Beyond inodes

While inodes serve as an effective vehicle to introduce these three patterns they do not display the full scope of any of them so it is useful to look further afield and see what else we can learn.

A survey of the use of unions elsewhere in the kernel shows that they are widely used though in very different circumstances than in struct inode. The particular aspect of inodes that is missing elsewhere is that a wide range of different modules (different filesystems) each wanted to extend an inode in different ways. In most places where unions are used there are a small fixed number of subtypes of the base type and there is little expectation of more being added. A simple example of this is struct nfs_fattr which stores file attribute information decoded out of an NFS reply. The details of these attributes are slightly different for NFSv2 and NFSv3 so there are effectively two subtypes of this structure with the difference encoded in a union. As NFSv4 uses the same information as NFSv3 this is very unlikely to ever be extended further.

A very common pattern in other uses of unions in Linux is for encoding messages that are passed around, typically between the kernel and user-space. struct siginfo is used to convey extra information with a signal delivery. Each signal type has a different type of ancillary information, so struct siginfo has a union to encode six different subtypes. union inputArgs appears to be the largest current union with 22 different subtypes. It is used by the "coda" network file system to pass requests between the kernel module and a user-space daemon which handles the network communication.

It is not clear whether these examples should be considered as the same pattern as the original struct inode. Do they really represent different subtypes of a base type, or is it just one type with internal variants? The Eiffel object-oriented programming language does not support variant types at all except through subtype inheritance so there is clearly a school of thought that would want to treat all usages of union as a form of subtyping. Many other languages, such as C++, provide both inheritance and unions allowing the programmer to make a choice. So the answer is not clear.

For our purposes it doesn't really matter what we call it as long as we know where to use each pattern. The examples in the kernel fairly clearly show that when all of the variants are understood by a single module, then a union is a very appropriate mechanism for variants structures, whether you want to refer to them as using data inheritance or not. When different subtypes are managed by different modules, or at least widely separate pieces of code, then one of the other mechanisms is preferred. The use of unions for this case has almost completely disappeared with only struct cycx_device remaining as an example of a deprecated pattern.

Problems with void pointers

Void pointers are not quite so easy to classify. It would probably be fair to say that void pointers are the modern equivalent of "goto" statements. They can be very useful but they can also lead to very convoluted designs. A particular problem is that when you look at a void pointer, like looking at a goto, you don't really know what it is pointing at. A void pointer called private is even worse - it is like a "goto destination" command - almost meaningless without reading lots of context.

Examining all the different uses that void pointers can be put to would be well beyond the scope of this article. Instead we will restrict our attention to just one new usage which relates to data inheritance and illustrates how the untamed nature of void pointers makes it hard to recognize their use in data inheritance. The example we will use to explain this usage is struct seq_file used by the seq_file library which makes it easy to synthesize simple text files like some of those in /proc. The "seq" part of seq_file simply indicates that the file contains a sequence of lines corresponding to a sequence of items of information in the kernel, so /proc/mounts is a seq_file which walks through the mount table reporting each mount on a single line.

When seq_open() is used to create a new seq_file it allocates a struct seq_file and assigns it to the private_data field of the struct file which is being opened. This is a straightforward example of void pointer based data inheritance where the struct file is the base type and the struct seq_file is a simple extension to that type. It is a structure that never exists by itself but is always the private_data for some file. struct seq_file itself has a private field which is a void pointer and it can be used by clients of seq_file to add extra state to the file. For example md_seq_open() allocates a struct mdstat_info structure and attaches it via this private field, using it to meet md's internal needs. Again, this is simple data inheritance following the described pattern.

However the private field of struct seq_file is used by svc_pool_stats_open() in a subtly but importantly different way. In this case the extra data needed is just a single pointer. So rather than allocating a local data structure to refer to from the private field, svc_pool_stats_open simply stores that pointer directly in the private field itself. This certainly seems like a sensible optimization - performing an allocation to store a single pointer would be a waste - but it highlights exactly the source of confusion that was suggested earlier: that when you look at a void pointer you don't really know what is it pointing at, or why.

To make it a bit clearer what is happening here, it is helpful to imagine "void *private" as being like a union of every different possible pointer type. If the value that needs to be stored is a pointer, it can be stored in this union following the "unions for data inheritance" pattern. If the value is not a single pointer, then it gets stored in allocated space following the "void pointers for data inheritance" pattern. Thus when we see a void pointer being used it may not be obvious whether it is being used to point to an extension structure for data inheritance, or being used as an extension for data inheritance (or being used as something else altogether).

To highlight this issue from a slightly different perspective it is instructive to examine struct v4l2_subdev which represents a sub-device in a video4linux device, such as a sensor or camera controller within a webcam. According to the (rather helpful) documentation it is expected that this structure will normally be embedded in a larger structure which contains extra state. However this structure still has not just one but two void pointers, both with names suggesting that they are for private use by subtypes:

/* pointer to private data */ void *dev_priv; void *host_priv;

It is common that a v4l sub-device (a sensor, usually) will be realized by, for example, an I2C device (much as a block device which stores your filesystem might be realized by an ATA or SCSI device). To allow for this common occurrence, struct v4l2_subdev provides a void pointer (dev_priv), so that the driver itself doesn't need to define a more specific pointer in the larger structure which struct v4l2_subdev would be embedded in. host_priv is intended to point back to a "parent" device such as a controller which acquires video data from the sensor. Of the three drivers which use this field, one appears to follow that intention while the other two use it to point to an allocated extension structure. So both of these pointers are intended to be used following the "unions for data inheritance" pattern, where a void pointer is playing the role of a union of many other pointer types, but they are not always used that way.

It is not immediately clear that defining this void pointer in case it is useful is actually a valuable service to provide given that the device driver could easily enough define its own (type safe) pointer in its extension structure. What is clear is that an apparently "private" void pointer can be intended for various qualitatively different uses and, as we have seen in two different circumstances, they may not be used exactly as expected.

In short, recognizing the "data inheritance through void pointers" pattern is not easy. A fairly deep examination of the code is needed to determine the exact purpose and usage of void pointers.

A diversion into struct page

Before we leave unions and void pointers behind a look at struct page may be interesting. This structure uses both of these patterns, though they are hidden somewhat due to historical baggage. This example is particularly instructive because it is one case where struct embedding simply is not an option.

In Linux memory is divided into pages, and these pages are put to a variety of different uses. Some are in the "page cache" used to store the contents of files. Some are "anonymous pages" holding data used by applications. Some are used as "slabs" and divided into pieces to answer kmalloc() requests. Others are simply part of a multi-page allocation or maybe are on a free list waiting to be used. Each of these different use cases could be seen as a subtype of the general class of "page", and in most cases need some dedicated fields in struct page, such as a struct address_space pointer and index when used in the page cache, or struct kmem_cache and freelist pointers when used as a slab.

Each page always has the same struct page describing it, so if the effective type of the page is to change - as it must as the demands for different uses of memory change over time - the type of the struct page must change within the lifetime of that structure. While many type systems are designed assuming that the type of an object is immutable, we find here that the kernel has a very real need for type mutability. Both unions and void pointers allow types to change and as noted, struct page uses both.

At the first level of subtyping there are only a small number of different subtypes as listed above; these are all known to the core memory management code, so a union would be ideal here. Unfortunately struct page has three unions with fields for some subtypes spread over all three, thus hiding the real structure somewhat.

When the primary subtype in use has the page being used in the page cache, the particular address_space that it belongs to may want to extend the data structure further. For this purpose there is a private field that can be used. However it is not a void pointer but is an unsigned long. Many places in the kernel assume an unsigned long and a void * are the same size and this is one of them. Most users of this field actually store a pointer here and have to cast it back and forth. The "buffer_head" library provides macros attach_page_buffers and page_buffers to set and get this field.

So while struct page is not the most elegant example, it is an informative example of a case where unions and void pointers are the only option for providing data inheritance.

The details of structure embedding

Where structure embedding can be used, and where the list of possible subtypes is not known in advance, it seems to be increasingly the preferred choice. To gain a full understanding of it we will again need to explore a little bit further than inodes and contrast data inheritance with other uses of structure embedding.

There are essentially three uses for structure embedding - three reasons for including a structure within another structure. Sometimes there is nothing particularly interesting going on. Data items are collected together into structures and structures within structures simply to highlight the closeness of the relationships between the different items. In this case the address of the embedded structure is rarely taken, and it is never mapped back to the containing structure using container_of().

The second use is the data inheritance embedding that we have already discussed. The third is like it but importantly different. This third use is typified by struct list_head and other structs used as an embedded anchor when creating abstract data types.

The use of an embedded anchor like struct list_head can be seen as a style of inheritance as the structure containing it "is-a" member of a list by virtue of inheriting from struct list_head. However it is not a strict subtype as a single object can have several struct list_heads embedded - struct inode has six (if we include the similar hlist_node). So it is probably best to think of this sort of embedding more like a "mixin" style of inheritance. The struct list_head provides a service - that of being included in a list - that can be mixed-in to other objects, an arbitrary number of times.

A key aspect of data inheritance structure embedding that differentiates it from each of the other two is the existence of a reference counter in the inner-most structure. This is an observation that is tied directly to the fact that the Linux kernel uses reference counting as the primary means of lifetime management and so would not be shared by systems that used, for example, garbage collection to manage lifetimes.

In Linux, every object with an independent existence will have a reference counter, sometimes a simple atomic_t or even an int, though often a more explicit struct kref. When an object is created using several levels of inheritance the reference counter could be buried quite deeply. For example a struct usb_device embeds a struct device which embeds struct kobject which has a struct kref. So usb_device (which might in turn be embedded in a structure for some specific device) does have a reference counter, but it is contained several levels down in the nest of structure embedding. This contrasts quite nicely with a list_head and similar structures. These have no reference counter, have no independent existence and simply provide a service to other data structures.

Though it seems obvious when put this way, it is useful to remember that a single object cannot have two reference counters - at least not two lifetime reference counters (It is fine to have two counters like s_active and s_count in struct super_block which count different things). This means that multiple inheritance in the "data inheritance" style is not possible. The only form of multiple inheritance that can work is the mixin style used by list_head as mentioned above.

It also means that, when designing a data structure, it is important to think about lifetime issues and whether this data structure should have its own reference counter or whether it should depend on something else for its lifetime management. That is, whether it is an object in its own right, or simply a service provided to other objects. These issues are not really new and apply equally to void pointer inheritance. However an important difference with void pointers is that it is relatively easy to change your mind later and switch an extension structure to be a fully independent object. Structure embedding requires the discipline of thinking clearly about the problem up front and making the right decision early - a discipline that is worth encouraging.

The other key telltale for data inheritance structure embedding is the set of rules for allocating and initializing new instances of a structure, as has already been hinted at. When union or void pointer inheritance is used the main structure is usually allocated and initialized by common code (the mid-layer) and then a device specific open() or create() function is called which can optionally allocate and initialize any extension object. By contrast when structure embedding is used the structure needs to be allocated by the lowest level device driver which then initializes its own fields and calls in to common code to initialize the common fields.

Continuing the struct inode example from above which has an alloc_inode() method in the super_block to request allocation, we find that initialization is provided for with inode_init_once() and inode_init_always() support functions. The first of these is used when the previous use of a piece of memory is unknown, the second is sufficient by itself when we know that the memory was previously used for some other inode. We see this same pattern of an initializer function separate from allocation in kobject_init(), kref_init(), and device_initialize().

So apart from the obvious embedding of structures, the pattern of "data inheritance through structure embedding" can be recognized by the presence of a reference counter in the innermost structure, by the delegation of structure allocation to the final user of the structure, and by the provision of initializing functions which initialize a previously allocated structure.

Conclusion

In exploring the use of method dispatch (last week) and data inheritance (this week) in the Linux kernel we find that while some patterns seem to dominate they are by no means universal. While almost all data inheritance could be implemented using structure embedding, unions provide real value in a few specific cases. Similarly while simple vtables are common, mixin vtables are very important and the ability to delegate methods to a related object can be valuable.

We also find that there are patterns in use with little to recommend them. Using void pointers for inheritance may have an initial simplicity, but causes longer term wastage, can cause confusion, and could nearly always be replaced by embedded inheritance. Using NULL pointers to indicate default behavior is similarly a poor choice - when the default is important there are better ways to provide for it.

But maybe the most valuable lesson is that the Linux kernel is not only a useful program to run, it is also a useful document to study. Such study can find elegant practical solutions to real problems, and some less elegant solutions. The willing student can pursue the former to help improve their mind, and pursue the latter to help improve the kernel itself. With that in mind, the following exercises might be of interest to some.

Exercises

As inodes now use structure embedding for inheritance, void pointers should not be necessary. Examine the consequences and wisdom of removing "i_private" from "struct inode".

Rearrange the three unions in struct page to just one union so that the enumeration of different subtypes is more explicit.

As was noted in the text, struct seq_file can be extended both through "void pointer" and a limited form of "union" data inheritance. Explain how seq_open_private() allows this structure to also be extended through "embedded structure" data inheritance and give an example by converting one usage in the kernel from "void pointer" to "embedded structure". Consider submitting a patch if this appears to be an improvement. Contrast this implementation of embedded structure inheritance with the mechanism used for inodes.

Though subtyping is widely used in the kernel, it is not uncommon for a object to contain fields that not all users are interested in. This can indicate that more fine grained subtyping is possible. As very many completely different things can be represented by a "file descriptor", it is likely that struct file could be a candidate for further subtyping.

Identify the smallest set of fields that could serve as a generic struct file and explore the implications of embedding that in different structures to implement regular files, socket files, event files, and other file types. Exploring more general use of the proposed open() method for inodes might help here.

Identify an "object-oriented" language which has an object model that would meet all the needs of the Linux kernel as identified in these two articles.

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zoho.com : https://docs.zoho.com/file/5j7aqec6140d5e2c64658b5949934897c142b

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Vendor	:	IBM
Exam Code	:	000-833
Exam Name	:	Object Oriented Analysis and Design - Part 1 (Analysis)
Questions and Answers	:	50 Q & A
Updated On	:	February 22, 2019
PDF Download Mirror	:	Pass4sure 000-833 Dump
Get Full Version	:	Pass4sure 000-833 Full Version

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