CS CS 5150 Software Engineering Lecture 15 Program Design 1

CS 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 Comments on Assignment 2: Schedules The schedule must provide time for: User testing and revisions Program and system testing Revision and correction of problems discovered during testing Deployment Handover and acceptance testing

CS Architectural Style - Model/View/Controller Model Controller View Example: Control of a unmanned model aircraft Controller: Receives instrument readings from the aircraft and sends controls signals to the aircraft. Model: Translates data received from and sent to the aircraft, and instructions from the user into a model of flight performance. Uses domain knowledge about the aircraft and flight. View: Displays information about the aircraft to the user and transmits instructions to the model.

CS Model/View/Controller: Autonomous Land Vehicle Sensors GPS Sonar Laser Signal processing ModelControl signals Steer Throttle Controls ViewModelController

CS Model/View/Controller for Web Applications 1User interacts with the user interface (e.g., presses a mouse button). 2Controller handles input event from the user interface, (e.g., via a registered handler or callback) and converts the event into appropriate user action. 3Controller notifies Model of user action, possibly resulting in a change in Model's state (e.g., update shopping cart.). 4View interacts with Model to generate an appropriate user interface response (e.g., list shopping cart's contents). 5User interface waits for further user interactions. from Wikipedia 10/18/2009

CS Model/View/Controller for Web Applications ModelControllerView HTMLHTTP WebBrowser control functions WebBrowser view functions Input events Response

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

CS 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 (where not part of the system architecture) algorithms, data structures, security mechanisms, operational procedures If the program design is done properly, all design decisions should be made before implementation.

CS 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. 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 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 The "Hello, World!" Applet import java.awt.Graphics; class HelloWorld extends java.applet.Applet { public void paint (Graphics g) { g.drawString ("Hello, World!", 10, 10); } Example from: BJR

CS The HelloWorld Example HelloWorld paint() class name operations

CS Abstraction for HelloWorld HelloWorld paint() g.drawString ("HelloWorld", 0, 10)" class name operations annotation

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

CS Rational Rose: A Typical Class Diagram

CS Specification Fields

CS General Specification Fields

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

CS Relationships ParkingLot ParkingSpace location is_available() *

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

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

CS Notation: Interface 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. ISpelling

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

CS Packaging Classes applet awt lang HelloWorld java Graphics package

CS 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 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 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 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 Candidate Classes Librarythe name of the system Book Journal Copy ShortTermLoanevent LibraryMember Weekmeasure MemberOfLibraryrepeat Itembook or journal Timeabstract term MemberOfStaff Systemgeneral term Rulegeneral term

CS Relations between Classes Bookis anItem Journalis anItem Copyis a copy of a Book LibraryMember Item MemberOfStaffis aLibraryMember Is Item needed?

CS Operations LibraryMemberborrowsCopy LibraryMemberreturnsCopy MemberOfStaffborrowsJournal MemberOfStaffreturnsJournal Item not needed yet.

CS A Possible Class Diagram MemberOfStaffBookCopyJournal is a copy of 1..* 1 LibraryMember 1 0..* on loan

CS 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 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 Rough Sketch: Wholesale System Design is empirical and iterative. The following very artificial example, gives an idea of the process. Example A wholesale merchant supplies retail stores from stocks of goods in a warehouse. What classes would you use to model this business?

CS Rough Sketch: Wholesale System RetailStore Warehouse Order Invoice Product Shipment Merchant

CS Rough Sketch: Wholesale System Warehouse Order Invoice Product Merchant RetailStore name address contactInfo financialInfo Shipment Responsibilities -track status of shipped products Reversal damaged() return() wrongItem() responsibility (text field)

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

CS Modeling Invoice Shipment Invoice invoiceNumber +goodsShipped() -sendInvoice() goodsShipped PartsList adornments + public - private RetailStore ??? invoiceRecord

CS 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 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 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 Exam Question: Candidate Classes Systemgeneral term WeatherMap Datasame as MeteorologicalData WeatherStationis this a general term? MeteorologicalDatahow does this relate to WeatherStation? DataSummaryhow does this relate to MeteorologicalData? AreaComputerhardware Databasegeneral term DigitizedMap

CS Exam Question: Observations about the Candidate Classes WeatherMapis a DigitizedMap is derived from 1...* DataSummary WeatherStationhas a set of MeteorologicalData MeteorologicalData DataSummaryis derived from MeteorologicalData DigitizedMap Can Meteorological Data be an attribute of WeatherStation? Can DataSummary be combined with WeatherMap?

CS Exam Question: Attributes and Operations WeatherStation location metereologicalData collectData() getSummary() WeatherMap location date-time geographicData weather gatherData() printMap() DigitizedMap location geographicData printMap() Or should MetereologicalData be a separate object?

CS Exam Question: Class Diagram DigitizedMap 1...* 1 WeatherStation location metereologicalData collectData() getSummary() WeatherMap location date-time geographicData weather gatherData() printMap() summary *