CS 501 Software Engineering Lectures 15 16 Object

CS 501: Software Engineering Lectures 15 & 16 Object Oriented Design 1 & 2 1 CS 501 Spring 2006

Administration Quiz 3 is on Thursday No office hours on Thursday 2 CS 501 Spring 2006

The Waterfall Model Requirements Analysis System design Design Program design Implementation Coding Unit & Integration Testing System Testing Acceptance Testing Operation & Maintenance 3 CS 501 Spring 2006

Program Design The task of program design is to represent the software system functions in a form that can be transformed into one or more executable programs. Given a system architecture, the program design specifies: • programs, components, packages, classes and class hierarchies • interfaces, protocols • security mechanisms, operational procedures UML models (diagrams and specifications) can be used for almost all aspects of program design 4 CS 501 Spring 2006

Models: Levels of Abstraction The complexity of a model depends on its level of abstraction: • High-levels of abstraction show the overall system. • Low-levels of abstraction are needed for implementation. Two approaches: 5 • Model entire system at same level of abstraction, but present diagrams with different levels of detail. • Model parts of system at different levels of abstraction. CS 501 Spring 2006

UML Models A UML model consists of: (a) A diagram. This gives a general overview of the model, showing the principal elements and how they relate to each other. A diagram is the graphical representation of a set of elements, usually rendered as a connected graph of vertices (things) and arcs (relationships). (b) A specification. This provides details about each element of the model. Specification for models used in program design should have sufficient detail that they can be used to write code from. 6 CS 501 Spring 2006

List of all Diagrams in UML • Use case diagram shows a set of use cases and actors (a special kind of class) and their relationships. Principally used for requirements. • Component diagram shows the organization and dependencies among a set of components. Principally used for system architecture. • Deployment diagram shows the configuration of processing nodes and the components that live on them. Principally used for system architecture. 7 CS 501 Spring 2006

List of all Diagrams in UML These models are used principally for program design. • Class diagram shows a set of classes, interfaces, and collaborations with their relationships. • Object diagram shows a set of objects and their relationships. 8 CS 501 Spring 2006

List of all Diagrams in UML These models are for interactive aspects of systems. They can be used for requirements or program design. 9 • Interaction diagrams: set of objects and their relationships including messages that may be dispatched among them => Sequence diagrams: time ordering of messages => Collaboration diagrams: structural organization of objects that send and receive messages • Statechart diagram shows a state machine consisting of states, transitions, events, and activities. • Activity diagram is a statechart diagram that shows the flow from activity to activity within a system. CS 501 Spring 2006

Using Rational Rose for Program Design 10 CS 501 Spring 2006

Class Diagrams Window origin size open() close() move() display() name attributes operations responsibilities (optional text) A class is a description of a set of objects that share the same attributes, operations, relationships and semantics. 11 CS 501 Spring 2006

A Typical Class Diagram 12 CS 501 Spring 2006

Another Typical Design 13 CS 501 Spring 2006

Specification 14 CS 501 Spring 2006

Specification Fields 15 CS 501 Spring 2006

General Specification Fields 16 CS 501 Spring 2006

The "Hello, World!" Example import java. awt. Graphics; class Hello. World extends java. applet. Applet { public void paint (Graphics g) { g. draw. String ("Hello, World!", 10); } } Example from: BJR 17 CS 501 Spring 2006

The Hello. World Example class name Hello. World operations paint() 18 CS 501 Spring 2006

Abstraction for Hello. World class name Hello. World operations paint() 19 annotation g. draw. String ("Hello. World", 0, 10)" CS 501 Spring 2006

Annotation some text note A note is a symbol for rendering constraints and comments attached to an element or a collection of elements. 20 CS 501 Spring 2006

Notation: Grouping Business rules A package is a general-purpose mechanism for organizing elements into groups. 21 CS 501 Spring 2006

Packaging Classes java Hello. World applet Graphics awt package lang 22 CS 501 Spring 2006

Notation: Relationships A dependency is a semantic relationship between two things in which a change to one may effect the semantics of the other. 0. . 1 employer * employee An association is a structural relationship that describes a set of links, a link being a connection among objects. 23 CS 501 Spring 2006

Relationships Parking 1 0. . . 1 Parking. Space location is_available() 24 CS 501 Spring 2006

Notation: Relationships (continued) child parent A generalization is a specialization/generalization relationship is which objects of the specialized element (child) are substitutable for objects of the generalized element (parent). 25 A realization is a semantic relationship between classifiers, wherein one classifier specifies a contract that another classifier guarantees to carry out. CS 501 Spring 2006

Generalization Applet generalization Note that the Applet and Graphics classes are shown elided, i. e. , just the name is shown, not the attributes or operations. Hello. World paint() 26 dependency Graphics CS 501 Spring 2006

Notation: Interface ISpelling An interface is a collection of operations that specify a service of a class or component, i. e. , the externally visible behavior of that element. 27 CS 501 Spring 2006

Class Inheritance Diagram Object Panel interface Component Image. Observer Applet Container Hello. World 28 CS 501 Spring 2006

Modeling Classes Given a real-life system, how do you decide what classes to use? 29 • What terms do the users and implementers use to describe the system? They are candidates for classes. • Is each candidate class crisply defined? • For each class, what is its set of responsibilities? Are the responsibilities evenly balanced among the classes? • What attributes and operations does each class need to carry out its responsibilities? CS 501 Spring 2006

Coupling and Cohesion Coupling is a measure of the dependencies between two subsystems. If two systems are strongly coupled, it is hard to modify one without modifying the other. Cohesion is a measure of dependencies within a subsystem. If a subsystem contains many closely related functions its cohesion is high. Aim for high cohesion within classes and weak coupling between them. 30 CS 501 Spring 2006

Candidate Classes: Application Classes and Solution Classes Application classes and solution classes: Application classes represent application concepts. Noun identification is an effective technique to generate candidate application classes. Solution classes represent system concepts, e. g. , user interface objects, databases, etc. 31 CS 501 Spring 2006

Noun Identification: A Library Example The library contains books and journals. It may have several copies of a given book. Some of the books are reserved for short-term loans only. All others may be borrowed by any library member for three weeks. Members of the library can normally borrow up to six items at a time, but members of staff may borrow up to 12 items at one time. Only members of staff may borrow journals. The system must keep track of when books and journals are borrowed and returned and enforce the rules. 32 CS 501 Spring 2006

Noun Identification: A Library Example The library contains books and journals. It may have several copies of a given book. Some of the books are reserved for short-term loans only. All others may be borrowed by any library member for three weeks. Members of the library can normally borrow up to six items at a time, but members of staff may borrow up to 12 items at one time. Only members of staff may borrow journals. The system must keep track of when books and journals are borrowed and returned and enforce the rules. 33 CS 501 Spring 2006

Candidate Classes Library Book Journal Copy Short. Term. Loan Library. Member Week Member. Of. Library Item Time Member. Of. Staff System Rule 34 the name of the system event measure repeat book or journal abstract term general term CS 501 Spring 2006

Relations between Classes Book Journal Copy Library. Member Item Member. Of. Staff is an is a copy of a Item Book is a Library. Member Is Item needed? 35 CS 501 Spring 2006

Operations Library. Member borrows Copy Library. Member returns Copy Member. Of. Staff borrows Journal Member. Of. Staff returns Journal Item not needed yet. 36 CS 501 Spring 2006

Class Diagram Member. Of. Staff Library. Member 1 1 on loan 0. . 12 Journal 0. . * Copy is a copy of 1. . * 37 Book 1 CS 501 Spring 2006

Rough Sketch: Wholesale System A wholesale merchant supplies retail stores from stocks of goods in a warehouse. What classes would you use to model this business? 38 CS 501 Spring 2006

Rough Sketch: Wholesale System Retail. Store Order Merchant Product Warehouse Invoice 39 Shipment CS 501 Spring 2006

Rough Sketch: Wholesale System Retail. Store name address contact. Info financial. Info Merchant Warehouse Order Product Reversal Invoice 40 Shipment damaged() return() wrong. Item() Responsibilities -track status of shipped products responsibility (text field) CS 501 Spring 2006

Expanding a Class: Modeling Financial Information Retail. Store association 1 * Transaction Which class is responsible for the financial records for a store? 41 Payment Invoice CS 501 Spring 2006

Modeling Invoice Shipment ? ? ? Retail. Store invoice. Record goods. Shipped Invoice invoice. Number Parts. List adornments +goods. Shipped() + public -send. Invoice() - private 42 CS 501 Spring 2006

Lessons Learned Design is empirical. There is no single correct design. During the design process: • Eliding: Elements are hidden to simplify the diagram • Incomplete: Elements may be missing. • Inconsistency: The model may not be consistent The diagram is not the whole design. Diagrams must be backed up with specifications. 43 CS 501 Spring 2006

From Candidate Classes to Completed Design Methods used to move to final design: Reuse: Wherever possible use existing components, or class libraries. They may need modification. Restructuring: Change the design to improve, understandability, maintainability, etc. Techniques include merging similar classes, splitting complex classes, etc. Optimization: Ensure that the system meets anticipated performance requirements, e. g. , by changed algorithms or restructuring. Completion: Fill all gaps, specify interfaces, etc. 44 CS 501 Spring 2006

An Exam Question: Object Oriented Design A system generates weather maps using data collected from unattended weather stations. Each weather station collects meteorological data and produces summaries of the data. On request, it sends the summary information to an area computer. The area computer uses a database of digitized maps to generate a set of local weather maps. 45 CS 501 Spring 2006

Exam Question: Noun Identification A system generates weather maps using data collected from unattended weather stations. Each weather station collects meteorological data and produces summaries of the data. On request, it sends the summary information to an area computer. The area computer uses a database of digitized maps to generate a set of local weather maps. 46 CS 501 Spring 2006

Exam Question: Candidate Classes System general term Weather. Map Data same as Meteorological. Data Weather. Station is this a general term? Meteorological. Data how does this relate to Weather. Station? Data. Summary how does this relate to Meteorological. Data? Area. Computer hardware Database general term Digitized. Map 47 CS 501 Spring 2006

Exam Question: Observations about the Candidate Classes Weather. Map is a Digitized. Map is derived from 1. . . * Data. Summary Weather. Station has a set of Meteorological. Data. Summary is derived from Meteorological. Data Digitized. Map Can Meteorological Data be an attribute of Weather. Station? Can Data. Summary be combined with Weather. Map? 48 CS 501 Spring 2006

Exam Question: Attributes and Operations Weather. Station location metereological. Data collect. Data() get. Summary() Digitized. Map location geographic. Data print. Map() 49 Weather. Map location date-time geographic. Data weather gather. Data() print. Map() Or should Metereological. Data be a separate object? CS 501 Spring 2006

Exam Question: Class Diagram Digitized. Map Weather. Station location metereological. Data collect. Data() get. Summary() Weather. Map 1 1. . . * summary location date-time geographic. Data weather gather. Data() print. Map() * 50 CS 501 Spring 2006