Copyright Flying Kiwi Productions Inc. 1 An Introduction to Object-Oriented Analysis Objects and UML in plain English. Chapter 12: Subsystems Based on the book by David William Brown John Wiley & Sons, ISBN

Copyright Flying Kiwi Productions Inc. 2 Copyright Copyright Flying Kiwi Productions All rights reserved. This slide presentation is based on “An Introduction to Object- Oriented Analysis; Objects and UML in Plain English,” by David William Brown, Wiley, ISBN , “The Book.” where a copy of The Book is purchased Permission is hereby granted to copy, modify or excerpt all or any part of this slide presentation, provided it is solely for use with courses, seminars or other presentations or productions where a copy of The Book is purchased by or for each and every participant or recipient. An instructor guide is available from the publisher for such presentations.

Copyright Flying Kiwi Productions Inc. 3 Chapter 12: Subsystems Dividing Up a Project How to Subdivide When to Subdivide Some Special Classes Comparison of Terms The Multilayer Model.

Copyright Flying Kiwi Productions Inc Dividing Up a Project. Chapter 12: Subsystems

Copyright Flying Kiwi Productions Inc. 5 l It can be used on projects n From very small, with 4 or 5 classes, n To huge, with hundreds of classes l But large projects are difficult to manage (in any paradigm) l Simply because of size and complexity. number of possible relationships The number of possible relationships exponentially grows exponentially with the number of classes. Chapter 12: Subsystems Chapter 12: Subsystems Dividing Up a Project. scalable OOA is highly scalable

Copyright Flying Kiwi Productions Inc. 6 l Can be physically impossible to draw, l Let alone comprehend. reduce complexity. We need to reduce complexity. Subsystems, One method is Subsystems, encapsulation. Which are a form of encapsulation. Chapter 12: Subsystems Chapter 12: Subsystems Dividing Up a Project. l l A large system with hundreds of boxes on the diagram

Copyright Flying Kiwi Productions Inc. 7 Encapsulation is hiding details and complexity within a well-defined published boundary. Chapter 12: Subsystems Chapter 12: Subsystems Dividing Up a Project. As we have defined it

Copyright Flying Kiwi Productions Inc. 8 To illustrate, here is a class diagram for a Human Resources system... Chapter 12: Subsystems Chapter 12: Subsystems Dividing Up a Project.

Copyright Flying Kiwi Productions Inc. 9 Skill Requirement Position Assignment Chapter 12: Subsystems Chapter 12: Subsystems Dividing Up a Project. Project Unit of Work Activity Employee Position Enrolment Credential Skill Course Training Source Instructor Course Offering H.R. System Licence drives 1 * 1 * 1 * * 1 * * ** * 11 * 1 * * **1 1 * 1 * * * * * 1 * ** 1 * * 1 * 1 ** * * * 1 * 1

Copyright Flying Kiwi Productions Inc. 10 Such as the Time-Reporting System... Chapter 12: Subsystems Chapter 12: Subsystems Dividing Up a Project. We can divide this diagram into clusters of related classes,

Copyright Flying Kiwi Productions Inc. 11 TimeReporting Skill Requirement Position Assignment Chapter 12: Subsystems Chapter 12: Subsystems Dividing Up a Project. Project Unit of Work Activity Employee Position Enrolment Credential Skill Course Training Source Instructor Course Offering H.R. System Licence drives 1 * 1 * 1 * * 1 * * ** * 11 * 1 * * **1 1 * 1 * * * * * 1 * ** 1 * * 1 * 1 ** * * * 1 * 1

Copyright Flying Kiwi Productions Inc. 12 Chapter 12: Subsystems Chapter 12: Subsystems Dividing Up a Project. And the Administration System...

Copyright Flying Kiwi Productions Inc. 13 AdministrationSubsystem Skill Requirement Position Assignment Chapter 12: Subsystems Chapter 12: Subsystems Dividing Up a Project. Project Unit of Work Activity Employee Position Enrolment Credential Skill Course Training Source Instructor Course Offering H.R. System Licence drives 1 * 1 * 1 * * 1 * * ** * 11 * 1 * * **1 1 * 1 * * * * * 1 * ** 1 * * 1 * 1 ** * * * 1 * 1

Copyright Flying Kiwi Productions Inc. 14 Chapter 12: Subsystems Chapter 12: Subsystems Dividing Up a Project. And the Skills & Training System...

Copyright Flying Kiwi Productions Inc. 15 Skills & Training Subsystem Skill Requirement Position Assignment Chapter 12: Subsystems Chapter 12: Subsystems Dividing Up a Project. Project Unit of Work Activity Employee Position Enrolment Credential Skill Course Training Source Instructor Course Offering H.R. System Licence drives 1 * 1 * 1 * * 1 * * ** * 11 * 1 * * **1 1 * 1 * * * * * 1 * ** 1 * * 1 * 1 ** * * * 1 * 1

Copyright Flying Kiwi Productions Inc. 16 Chapter 12: Subsystems Chapter 12: Subsystems Dividing Up a Project. can be viewed as a sub -sub-system... Of which the Training part

Copyright Flying Kiwi Productions Inc. 17 TrainingSub-sub-system Skill Requirement Position Assignment Chapter 12: Subsystems Chapter 12: Subsystems Dividing Up a Project. Project Unit of Work Activity Employee Position Enrolment Credential Skill Course Training Source Instructor Course Offering H.R. System Licence drives 1 * 1 * 1 * * 1 * * ** * 11 * 1 * * **1 1 * 1 * * * * * 1 * ** 1 * * 1 * 1 ** * * * 1 * 1

Copyright Flying Kiwi Productions Inc. 18 There are relatively few that cross the boundaries. Chapter 12: Subsystems Chapter 12: Subsystems Dividing Up a Project. Note that while there are many relationships within each subsystem,

Copyright Flying Kiwi Productions Inc. 19 Skill Requirement Position Assignment Chapter 12: Subsystems Chapter 12: Subsystems Dividing Up a Project. Project Unit of Work Activity Employee Position Enrolment Credential Skill Course Training Source Instructor Course Offering H.R. System Licence drives 1 * 1 * 1 * * 1 * * ** * 11 * 1 * **1 1 * 1 * * * * * 1 * * 1 * * 1 * 1 ** * * * 1 * 1 Skills & Training Subsystem Training Sub-sub-system 1*1 * ** * 1 1 * 1 *

Copyright Flying Kiwi Productions Inc. 20 The human mind can handle only “Seven  Three” pieces of information (Miller 1956,1975) Chapter 12: Subsystems Chapter 12: Subsystems Dividing Up a Project. The Purpose of Subsystems

Copyright Flying Kiwi Productions Inc. 21 complexity There is a definite limit to the amount of complexity we can handle. dividedencapsulated Models divided and encapsulated become More understandable, More understandable, and Better communication tools. Chapter 12: Subsystems Chapter 12: Subsystems Dividing Up a Project. In other words,

Copyright Flying Kiwi Productions Inc. 22 Let’s look at how to go and do this... Chapter 12: Subsystems Chapter 12: Subsystems Dividing Up a Project. Now we’ve seen what subsystems are about,

Copyright Flying Kiwi Productions Inc. 23 Chapter 12: Subsystems Dividing Up a Project How to Subdivide When to Subdivide Some Special Classes Comparison of Terms The Multilayer Model.

Copyright Flying Kiwi Productions Inc How to Subdivide. Chapter 12: Subsystems

Copyright Flying Kiwi Productions Inc. 25 l Often the divisions are “obvious”, l But still check the other criteria on the next few slides... Chapter 12: Subsystems Chapter 12: Subsystems How to Subdivide. Intuitively Obvious

Copyright Flying Kiwi Productions Inc. 26 l For a subsystem to be an identifiable unit or whole, l Relatively few connections should cross its boundaries. l These connections can be: n Associations from the Class Diagram, n Events passed from one state machine to another (Ch 10), n Messages passed to a class requesting a service, n Responsibilities borne by one class to another. Chapter 12: Subsystems Chapter 12: Subsystems How to Subdivide. Minimal Interactions and Dependencies

Copyright Flying Kiwi Productions Inc. 27 l Our example showed subsystems for n Training n Skills & Training n Time Reporting n Personnel Administration n And so on. l Each exists to handle some Business Function. Chapter 12: Subsystems Chapter 12: Subsystems How to Subdivide. Functional Grouping

Copyright Flying Kiwi Productions Inc. 28 l Sometimes the groupings will be by hardware/software function l e.g., Printing, GUI or Database subsystems. l Subsystems may also be set by things happening at a single n Geographical location, n Hardware platform. Chapter 12: Subsystems Chapter 12: Subsystems How to Subdivide. Functional Grouping

Copyright Flying Kiwi Productions Inc. 29 Chapter 12: Subsystems Dividing Up a Project How to Subdivide When to Subdivide Some Special Classes Comparison of Terms The Multilayer Model.

Copyright Flying Kiwi Productions Inc When to Subdivide. Chapter 12: Subsystems

Copyright Flying Kiwi Productions Inc. 31 Systems Request document Systems Request document n Your first encounter with the problem n Your experience allied with your users’ view of the problem Completion of Requirements Analysis Completion of Requirements Analysis n Pause at this point to check n Maybe reuse a subsystem from an earlier project. Chapter 12: Subsystems Chapter 12: Subsystems When to Subdivide. Before you begin Before you begin n n Based on knowledge of users’ business

Copyright Flying Kiwi Productions Inc. 32 Associations Associations show interactions and highlight collaborations l The Class Diagram is a powerful tool for finding subsystems graphic. Drawing a “fence” around a subsystem is easy, productive, and above all graphic. n Observe guidelines about “minimal interactions and dependencies.” l Works well at the whiteboard n Trying things out and erasing to try again. Chapter 12: Subsystems Chapter 12: Subsystems When to Subdivide. The Class Diagram The Class Diagram

Copyright Flying Kiwi Productions Inc. 33 n As you search for operations/services/methods n Using Use Cases, STDs, Responsibilities etc. n You will see groups of functions that belong together. Completion of Analysis n A final check. And at this stage an important use for subsystems... Chapter 12: Subsystems Chapter 12: Subsystems When to Subdivide. During Behavior Analysis During Behavior Analysis

Copyright Flying Kiwi Productions Inc. 34 skills data about? Who is this system recording skills data about? Chapter 12: Subsystems Chapter 12: Subsystems When to Subdivide. l l On the next slide, take a good look at Skills and Training the Skills and Training subsystem.

Copyright Flying Kiwi Productions Inc. 35 Employee Employee Skill Requirement Position Assignment Chapter 12: Subsystems Chapter 12: Subsystems Dividing Up a Project. Project Unit of Work Activity Position Enrolment Credential Skill Course Training Source Instructor Course Offering H.R. System Licence drives 1 * 1 * 1 * * 1 * * ** * 11 * 1 * **1 1 * 1 * * * * * 1 * * 1 * * 1 * 1 ** * * * 1 * 1 Skills & Training Subsystem Training Sub-sub-system *

Copyright Flying Kiwi Productions Inc. 36 The Employees, The Employees, of course. no Employee data So the Skills & Training subsystem wouldn’t work too well if there were no Employee data available. with or before So this means the Employee class must be built with or before the Skills & Training classes. But not only that... Chapter 12: Subsystems Chapter 12: Subsystems When to Subdivide. It’s keeping data about

Copyright Flying Kiwi Productions Inc. 37 Employee class Admin subsystem So the Employee class and the Admin subsystem ahead of need to be built ahead of the Skills & Training. But what about Chapter 12: Subsystems Chapter 12: Subsystems When to Subdivide. PositionSkill Requirement The link from Position to Skill Requirement shows that PositionPosition Assignment The Position and Position Assignment data must be in place for the Skills & Training system to work.  Time Reporting?... Position Skill Requirement

Copyright Flying Kiwi Productions Inc. 38 Chapter 12: Subsystems Chapter 12: Subsystems When to Subdivide. before or after Time Reporting could be built before or after the other subsystems, Employee Except that it requires the Employee class to be in place.

Copyright Flying Kiwi Productions Inc. 39 l By inspecting the models, especially the Class Diagram, must be in place you will see that certain classes or subsystems must be in place before the others can function. development sequence This determines the development sequence of the subsystems, Class Diagram and the Class Diagram can be a useful tool for discussion, understanding and decision-making with the users. Chapter 12: Subsystems Chapter 12: Subsystems When to Subdivide. So we are saying that

Copyright Flying Kiwi Productions Inc. 40 But some classes can be a little tricky... Chapter 12: Subsystems Chapter 12: Subsystems When to Subdivide.

Copyright Flying Kiwi Productions Inc. 41 Chapter 12: Subsystems Dividing Up a Project How to Subdivide When to Subdivide Some Special Classes Comparison of Terms The Multilayer Model.

Copyright Flying Kiwi Productions Inc Some Special Classes. Chapter 12: Subsystems

Copyright Flying Kiwi Productions Inc. 43 l Employee is the classic example. l Almost every project will need Employee data. l Let’s say that in your modeling, you discover and design an Employee class, l But the HR model already has one, l So you negotiate with the HR people, l And add the things you need to their existing class. Chapter 12: Subsystems Chapter 12: Subsystems Some Special Classes. Classes that appear in several subsystems

Copyright Flying Kiwi Productions Inc. 44 l During modeling, the users will often come up with a class that already exists in another model. l You must compare your definition, attributes and behaviors, which reflect the needs of your project, against the existing ones. Chapter 12: Subsystems Chapter 12: Subsystems Some Special Classes. Classes that appear in several subsystems

Copyright Flying Kiwi Productions Inc. 45 l Classes whose relationships or message links cross the boundary. l These decisions are not critical, But can cause heated discussion! But can cause heated discussion! l Don’t get into a big argument. l Make a decision and move on. Chapter 12: Subsystems Chapter 12: Subsystems Some Special Classes. Classes on the Boundaries

Copyright Flying Kiwi Productions Inc. 46 l Look for the subsystem to which this class has more relationship &/or message links. l Logically and intuitively, which subsystem (or set of users) does this class appear to belong to? l Which subsystem has to be built first? l Can it be built without this class? consensus l Judgment call, by team consensus (I can live with it...) Chapter 12: Subsystems Chapter 12: Subsystems Some Special Classes. Classes on the Boundaries

Copyright Flying Kiwi Productions Inc. 47 And now some discussion of word usage... Chapter 12: Subsystems Chapter 12: Subsystems Some Special Classes.

Copyright Flying Kiwi Productions Inc. 48 Chapter 12: Subsystems Dividing Up a Project How to Subdivide When to Subdivide Some Special Classes Comparison of Terms The Multilayer Model.

Copyright Flying Kiwi Productions Inc Comparison of Terms. Chapter 12: Subsystems

Copyright Flying Kiwi Productions Inc. 50 Definition: “A mechanism for guiding a reader.... through a large and complex model.” l Subjects (i.e. subsystems) are strictly a means to an end, l They give an overview of a complex model. l They are useful to both technical people (developers) and users. Chapter 12: Subsystems Chapter 12: Subsystems Comparison of Terms. Subjects - Coad & Yourdon

Copyright Flying Kiwi Productions Inc. 51 “Subsystem boundaries disappear at execution time.” do not show in the program code, l i.e., they do not show in the program code, l Only in the Analysis and Design models. Chapter 12: Subsystems Chapter 12: Subsystems Comparison of Terms. Rebecca Wirfs-Brock makes an important observation:

Copyright Flying Kiwi Productions Inc. 52 l They use the term “Domain” l By which they really mean “senior subsystems” l And which focuses on: Chapter 12: Subsystems Chapter 12: Subsystems Comparison of Terms. Shlaer & Mellor n n Problem domain, n n Software Architecture domain n n GUI domain n n Operating system domain n n etc. l l Firesmith(1993) considers the term “domain” possibly misleading and confusing.

Copyright Flying Kiwi Productions Inc. 53 l Prefers the term “subassemblies” components l Since they are components out of which the larger system is assembled. Chapter 12: Subsystems Chapter 12: Subsystems Comparison of Terms. Donald Firesmith

Copyright Flying Kiwi Productions Inc. 54 Chapter 12: Subsystems Dividing Up a Project How to Subdivide When to Subdivide Some Special Classes Comparison of Terms The Multilayer Model.

Copyright Flying Kiwi Productions Inc The Multilayer Model. Chapter 12: Subsystems

Copyright Flying Kiwi Productions Inc. 56 l Subsystems are a “vertical” sectioning of a model. l Think of this as standing above the model, reaching down with a knife held vertical to cut out each subsystem. horizontally If you run your “knife” horizontally through the model, l You divide it into“layers.” Chapter 12: Subsystems Chapter 12: Subsystems Comparison of Terms. Layers - Coad & Yourdon

Copyright Flying Kiwi Productions Inc. 57 l Think of layers as transparencies, l With part of your model on each, l So you can lay them on the model selectively, one of top of another l To show different parts of the model together. Chapter 12: Subsystems Chapter 12: Subsystems Comparison of Terms. Layers - Coad & Yourdon

Copyright Flying Kiwi Productions Inc. 58 Webster: thickness Webster: “One thickness... lying over or under another.” Coad & Yourdon: level of detail, Coad & Yourdon: “One level of detail, containing the results of a particular part of the Object- Oriented Analysis process, and it adds information to the other layers.” Chapter 12: Subsystems Chapter 12: Subsystems Comparison of Terms. Layers - Coad & Yourdon Definition:

Copyright Flying Kiwi Productions Inc. 59 l Subject/Subsystem layer l Class Diagram layer l Structure layer (Subclasses & Aggregations) l Attribute layer l Service/Operation/Behavior layer Chapter 12: Subsystems Chapter 12: Subsystems Comparison of Terms. The 5 Layers Coad & Yourdon

Copyright Flying Kiwi Productions Inc. 60 End of Chapter 12

Copyright Flying Kiwi Productions Inc. 61 End of Chapter 12

Copyright Flying Kiwi Productions Inc. 62 End of Chapter 12

Copyright Flying Kiwi Productions Inc. 63 End of Chapter 12

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