Internet-based Application Development -- copyright (c) 1998-2001 by Eric J. Braude 7/31/08-- Components -- page C.‹#›Comp 7700 – Design Principles II1Chapter 5Design Principles II:Flexibility, Reusability, and EfficiencyComp 7700 – Design Principles II2Process Phase Affected by This ChapterRequirementsAnalysisDesignImplementationArchitectureFramework Detailed DesignAdapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.Comp 7700 – Design Principles II3Aspects of Flexibility … adding more of the same kind of functionalityExample (banking application): handle more kinds of accountswithout having to change the existing design or code … adding different functionalityExample: add withdraw function to existing deposit functionality• … changing functionalityExample: allow overdraftsAnticipate …Adapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.Comp 7700 – Design Principles II4Registering Website MembersWebSiteregister()Member0..nmembersAdapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.Internet-based Application Development -- copyright (c) 1998-2001 by Eric J. Braude 7/31/08-- Components -- page C.‹#›Comp 7700 – Design Principles II5Registering Website Members FlexiblyWebSite Member0..nStandardMemberXMemberYMembermembersAdapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.Comp 7700 – Design Principles II6Adding Functionality to an Application:Alternative SituationsWithin the scope of … … a list of related functionsExample: add print to an air travel itinerary functions ... an existing base classExample: add “print road- and ship- to air itinerary ” ... neitherExample: add “print itineraries for combinations of air, road andship transportation”Adapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.Comp 7700 – Design Principles II7Adding Functionality When a BaseClass ExistsTripprintItinerary()StandardTripprintItinerary()SomeApplicationClassMethod(s) callprintItinerary()Adapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.Comp 7700 – Design Principles II8Adding Functionality Through a BaseClassTripprintItinerary()SeaTripprintItinerary()SomeApplicationClassLandTripprintItinerary()StandardTripprintItinerary()Adapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.Internet-based Application Development -- copyright (c) 1998-2001 by Eric J. Braude 7/31/08-- Components -- page C.‹#›Comp 7700 – Design Principles II9Additional Type of FlexibilityComponent technology –… configure objects of predefinedcomplex classes – or sets of classes –so as to interact in many waysComponent technology –… create and store a possibly complexobject of a class.“Behavioral” design patterns –… change, recombine, or otherwisecapture the mutual behavior of a set ofobjects“Structural” design patterns –… create variable trees of objects orother structures at runtime“Creational” design patterns –… create objects in variableconfigurations determined at runtimeDescribed in …Flexibility Aspect: ability to …Adapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.Comp 7700 – Design Principles II10Key Concept:  Flexibility We design flexibly, introducing parts,because change and reuse are likely.Adapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.Comp 7700 – Design Principles II11Making a Method Re-usable Specify completely– Preconditions etc– Avoid unnecessary coupling with the enclosing class– Make static if feasible– Include parameterization• i.e., make the method functional• But limit the number of parameters Make the names expressive– Understandability promotes re-usability Explain the algorithm– Re-users need to know how the algorithm worksAdapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.Comp 7700 – Design Principles II12Making a Class Re-usable Describe the class completely Make the class name and functionality matcha real world concept Define a useful abstraction– attain broad applicability Reduce dependencies on other classes– Elevate dependencies in hierarchyalternativesAdapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.Internet-based Application Development -- copyright (c) 1998-2001 by Eric J. Braude 7/31/08-- Components -- page C.‹#›Comp 7700 – Design Principles II13Reducing Dependency Among ClassesCustomerReplace …Pianowith …Customer PianoPianoOrderAdapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.Comp 7700 – Design Principles II14Leveraging Inheritance,Aggregation & Dependency for theRe-use of Class CombinationsCustomercomputeBill()RegularCustomercomputeBill()CustomercomputeBill()Billcompute()CustomercomputeBill( Orders )Ordersvalue()(1) Leveraging inheritance(3) Leveragingdependency(2) LeveragingaggregationCustomercomputeBill()Adapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.Comp 7700 – Design Principles II15Basic Approaches to Time Efficiency Design for Other Criteria, Then Consider Efficiency– Design for flexibility, reusability , …– At some point, identify inefficient places– Make targeted changes to improve efficiency Design for Efficiency From the Start– Identify key efficiency requirements up front– Design for these requirements during all phases Combine These Two Approaches– Make trade-offs for efficiency requirements during design– Address remaining efficiency issues after initial designAdapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.Comp 7700 – Design Principles II16Space-Time Trade-offsSpaceTime to process one itemTypical targetAdapted from Software Design: From Programming to Architecture by Eric J. Braude (Wiley 2003), with permission.Internet-based