CS 5150 Software Engineering Lecture 15 Object Oriented

CS 5150 Software Engineering Lecture 15 Object Oriented Design 1 CS 5150 1

Administration Test 3 is next Monday The test will cover material from all classes since the beginning of the semester, including next Monday's class. CS 5150 2

Project Presentations: Schedules The schedule must provide time for: • User testing • Program and system testing • Revision and correction of problems discovered during testing • Deployment • Handover and acceptance testing CS 5150 3

User Testing Design Analyze requirements User testing ? Build If you have two testing cycles, you have eight activities to schedule. CS 5150 4

Program Design in the Modified Waterfall Model Feasibility study Requirements System design Design Program design Implementation (coding) Testing Acceptance & release Operation & maintenance CS 5150 5

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 • algorithms, data structures, security mechanisms, operational procedures If the program design is done properly, all design decisions should be made before implementation. CS 5150 6

UML Models UML models (diagrams and specifications) can be used for almost all aspects of program design • Diagram 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). • Specification 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. CS 5150 7

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: • 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. This is usually a more effective use of effort. CS 5150 8

Choice of Models in UML • Use case model shows a set of use cases and actors (a special kind of class) and their relationships. Principally used for requirements. • Component model shows the organization and dependencies among a set of components. Principally used for system architecture. • Deployment model shows the configuration of processing nodes and the components that live on them. Principally used for system architecture. CS 5150 9

Choice of Models in UML Models that are used for program design: • Class model shows a set of classes, interfaces, and collaborations with their relationships. • Object model shows a set of objects and their relationships. CS 5150 10

Choice of Models in UML Models for interactive aspects of systems. They can be used for requirements or program design. • Statechart model shows a state machine consisting of states, transitions, events, and activities. • Activity model is a flow chart model that shows the flow from activity to activity within a system. • Interaction model: set of objects and their relationships including messages that may be dispatched among them => Sequence model: time ordering of messages CS 5150 11

Class Diagrams Window origin size open() close() move() display() name attributes [local, instance, and class (static) variables] operations [methods] responsibilities [optional text] A class is a description of a set of objects that share the same attributes, operations, relationships, and semantics. CS 5150 12

The "Hello, World!" Applet 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 CS 5150 13

The Hello. World Example class name Hello. World operations paint() CS 5150 14

Abstraction for Hello. World class name Hello. World operations paint() CS 5150 annotation g. draw. String ("Hello. World", 0, 10)" 15

Annotation some text note A note is a symbol for rendering constraints and comments attached to an element or a collection of elements. CS 5150 16

Rational Rose: A Typical Class Diagram CS 5150 17

Specification CS 5150 18

Specification Fields CS 5150 19

General Specification Fields CS 5150 20

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. CS 5150 21

Relationships Parking. Lot 1 1. . . * Parking. Space location is_available() CS 5150 22

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). A realization is a semantic relationship between classifiers, wherein one classifier specifies a contract that another classifier guarantees to carry out. CS 5150 23

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() CS 5150 dependency Graphics 24

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. CS 5150 25

Class Inheritance Diagram Object Component interface Image. Observer Container Panel Applet Hello. World CS 5150 26

Notation: Package Business rules A package is a general-purpose mechanism for organizing elements into groups. CS 5150 27

Packaging Classes java Hello. World applet Graphics awt package lang CS 5150 28

Modeling Classes Given a real-life system, how do you decide what classes to use? • 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 5150 29

Coupling and Cohesion Coupling is a measure of the dependencies between two part of a system. If two classes are strongly coupled, it is hard to modify one without modifying the other. Cohesion is a measure of dependencies within part of a system. If a class contains many closely related functions its cohesion is high. Aim for high cohesion within classes and weak coupling between them. CS 5150 30

Candidate 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. CS 5150 31

Noun Identification for Application Classes: 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. CS 5150 32

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. CS 5150 33

Candidate Classes Library Book Journal Copy Short. Term. Loan Library. Member Week Member. Of. Library Item Time Member. Of. Staff System Rule CS 5150 the name of the system event measure repeat book or journal abstract term general term 34

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? CS 5150 35

Operations Library. Member borrows Copy Library. Member returns Copy Member. Of. Staff borrows Journal Member. Of. Staff returns Journal Item not needed yet. CS 5150 36

A Possible Class Diagram Member. Of. Staff Library. Member 1 1 on loan 0. . 12 Journal 0. . * Copy is a copy of 1. . * CS 5150 Book 1 37

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? CS 5150 38

Rough Sketch: Wholesale System Retail. Store Order Merchant Product Warehouse Invoice CS 5150 Shipment 39

Rough Sketch: Wholesale System Retail. Store name address contact. Info financial. Info Merchant Warehouse Order Product Reversal Invoice CS 5150 Shipment Responsibilities -track status of shipped products responsibility (text field) damaged() return() wrong. Item() 40

Expanding a Class: Modeling Financial Information Retail. Store association 1 * Transaction Which class is responsible for the financial records for a store? CS 5150 Payment Invoice 41

Modeling Invoice Shipment ? ? ? Retail. Store invoice. Record goods. Shipped Invoice invoice. Number Parts. List adornments +goods. Shipped() + public -send. Invoice() - private CS 5150 42

Lessons Learned Design is empirical. There is no single correct design. During the design process: • Eliding: Elements are hidden to simplify the diagram • Incomplete: During the early part of the design process, elements may be missing. • Inconsistency: During the early part of the design process, the model may not be consistent The diagram is not the whole design. Diagrams must be backed up with specifications. CS 5150 43

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. CS 5150 44

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. CS 5150 45

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. CS 5150 46

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 CS 5150 47

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? CS 5150 48

Exam Question: Attributes and Operations Weather. Station location metereological. Data collect. Data() get. Summary() Digitized. Map location geographic. Data print. Map() CS 5150 Weather. Map location date-time geographic. Data weather gather. Data() print. Map() Or should Metereological. Data be a separate object? 49

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() * CS 5150 50