Frameworks IIIHow to use Application Frameworks“How to’s” for FrameworksSlide 4Slide 5Slide 6How to Learn Application FrameworksHow to Evaluate Application FrameworksHow to Develop Application FrameworksHooksHooks (cont’d)Benefits of FrameworksBenefits of Frameworks (cont’d)Classification of FrameworksSystem Infrastructure frameworksMiddleware Integration FrameworksEnterprise Application Frameworks1RRRFrameworks IIIPractical Issues2RRRHow to use Application Frameworks•Application developed with Framework has 3 parts:–framework–concrete subclasses–everything else: •script that specified which concrete classes will be used and how they will be interconnected•objects that have no relationship to framework•use one or more framework objects, but not called by framework objects3RRR“How to’s” for Frameworks•Use•Learn•Evaluate•Develop4RRRHow to use Application Frameworks•Easiest way: Blackbox (e.g., GUI frameworks)–connect existing components–DOES NOT change framework or make any new concrete subclasses–reuses framework’s interfaces and rules for connecting components–Analogous to:•Building from Legos•Connected integrated circuits for circuit board–Application programmers only need to know:•type A objects can be connected to type B objects•not need to know exact implementation of A and B5RRRHow to use Application Frameworks•Next easiest way: (Graybox)–Define new concrete subclasses; use them to build application–Subclasses are tightly coupled to superclasses:•Requires more knowledge about abstract classes–Subclasses must meet specification implied by superclasses•Programmer must understand framework’s interfaces in detail6RRRHow to use Application Frameworks•Most challenging way: (Whitebox)–Change the abstract classes that form core of framework•add new operations or variables to them–Analogous to fleshing out a skeleton of an application.–Usually requires the source code of framework–Most challenging, but most powerful–Changes to abstract classes can break existing concrete classes7RRRHow to Learn Application Frameworks•Learning a framework is more challenging than learning a class library–not just individual classes–learn a set of classes with specific interconnections–many classes are abstract•Must have concrete examples (easy to challenging)•Documentation should include:–Purpose of framework–How to use framework (e.g., cookbook style)–How the framework works :•interaction between objects•how responsibility is partitioned between objects8RRRHow to Evaluate Application Frameworks•Most application domains have no commercially available domain-specific frameworks•Criteria:–Run on “right” platform–“right” programming language–“right” standards–“right” tradeoffs between simplicity and power. •Make checklist for objectives of frameworks.–Features that must be supported (e.g., distributed, networking issues, interaction styles, etc.)9RRRHow to Develop Application Frameworks•Design of framework analogous to design of reusable SW–Domain analysis (collect examples)–First version: should implement examples•Usually whitebox–Then use to build applications•Will point out weak points in frameworks•Parts that are hard to change–Experience leads to improvements in framework•Make it more blackbox•Iteration is important:–Domain analysis will gain more information –Framework makes explicit the parts that will change•Components should implement changeable parts–Frameworks are abstractions•Design of framework depends on original examples10RRRHooks•Hook: Point in framework meant to be adapted–Filling in parameters–Creating subclasses•Hook Description:–Describes problem/requirement that framework builder anticipates application developer will have–Provides guidance as to how to use hook–Focuses on small requirement–Details required changes to design –Constraints to be satisfied–Effects on the framework11RRRHooks (cont’d)•Adaptation:–Enabling/disabling a feature–Replacing a feature–Augmenting a feature–Adding a feature12RRRBenefits of Frameworks•Modula r ity:–Encapsulate volatile implementation details behind stable interfaces–Localize impact of design/implementation changes •Reusa bility:–Stable interfaces enhance reusability of generic components–Leverages domain knowledge/prior experience•Extensib ility:–Hook methods that allow applications to extend its stable interfaces–Hook methods decouple stable interfaces and behaviors of an application domain13RRRBenefits of Frameworks (cont’d)•Inversion of Control:–Application processing customized by event handler objects •invoked via framework’s reactive dispatching mechanism–Allow framework (rather than each application) to determine which set of application-specific methods to invoke in response to external events •(e.g., window messages from end users or• packets arriving on communication ports)14RRRClassification of Frameworks•System Infrastructure•Middleware Integration •Enterprise application15RRRSystem Infrastructure frameworks•Simplify development of portable and efficient system infrastructure:•Examples:–OS (Campbell-Islam 93)–Communication (Schmidt 97)–UI and language processing tools•Primarily used internally within SW org16RRRMiddleware Integration Frameworks•Commonly used to integrate distributed applications and components•Designed to enhance ability of SW developers to modularize, reuse, and extend SW infrastructure in distributed environment•Examples:–ORB–Message-oriented MW–Transactional databases17RRREnterprise Application Frameworks•Address broad application domains:–E.g.: telecommunications, avionics, manufacturing, financial eng., •Expensive to develop/purchase•Good investment: –Support development of end-user applications/products directly•System Infrastructure/Middleware Frameworks:–Focus largely on internal SW development concerns–Contribute significantly to rapid creation of high-quality SW–Not contribute to high revenue for large business
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