R R R CSE870: Advanced Software Engineering: Frameworks (Cheng, Sp2003)1 Frameworks A Brief Introduction

R R R CSE870: Advanced Software Engineering: Frameworks (Cheng, Sp2003)2 Assigned Reading Designing Reusable Classes: Johnson and Foote (JOOP88) –Original Frameworks paper –Gives guidelines for creating frameworks –Motivates frameworks See Handouts and Links web page

R R R CSE870: Advanced Software Engineering: Frameworks (Cheng, Sp2003)3 Framework Support reuse of detailed designs An integrated set of components: –Collaborate to provide reusable architecture for –Family of related applications

R R R CSE870: Advanced Software Engineering: Frameworks (Cheng, Sp2003)4 Frameworks 1.Frameworks are semi-complete applications Complete applications are developed by inheriting from, and Instantiating parameterized framework components 2.Frameworks provide domain-specific functionality Ex.: business, telecommunication, dbases, distributed, OS kernels 3.Frameworks exhibit inversion of control at run-time Framework determines which objects and methods to invoke in response to events

R R R CSE870: Advanced Software Engineering: Frameworks (Cheng, Sp2003)5 Class Libraries vs Frameworks vs Patterns Definition: –Class Libraries: Self-contained, Pluggable ADTs –Frameworks: Reusable, semi- complete applications –Patterns: Problem, solution, context Application Specific Logic Networking Math Dbase ADTs UI Event Loop Application Specific Logic Math ADTs Event Loop UI Networking Dbase Invokes Call Backs Class Library Architecture Framework Architecture

R R R CSE870: Advanced Software Engineering: Frameworks (Cheng, Sp2003)6 Component Integration in Frameworks Framework components are loosely coupled via “callbacks” Callbacks allow independently developed software to be connected together Callbacks provide a connection-point –Generic framework objects communicate with application objects –Framework provides common template methods –Application provides the variant hook methods

R R R CSE870: Advanced Software Engineering: Frameworks (Cheng, Sp2003)7 Patterns vs Frameworks Patterns and frameworks play complementary, cooperative roles Patterns are more abstract descriptions of frameworks –Frameworks are implemented in specific language Complex frameworks may involve dozens of patterns Patterns may document frameworks

R R R CSE870: Advanced Software Engineering: Frameworks (Cheng, Sp2003)8 GUI Framework Model/View/Controller (MVC): –Smalltalk-80 UI framework UI: 3 types of components: –models, views, controllers –view and controller objects interacting with model Model: application object, UI-independent View: manages region of display –Keeps it consistent with state of model –Can be nested to form complex UIs Controller: converts user events (e.g., mouse movements and key presses) into operations on its model and view –Implement scrolling and menus

R R R CSE870: Advanced Software Engineering: Frameworks (Cheng, Sp2003)9 Example MVC Model: FileBrowser Views: –Top subview: String that is Pattern that matches set of files (e.g., *.h) –Middle subview: displays list of files that match pattern (e.g., Node.h, Int_node.h, etc.) –Bottom Subview: displays selected file –TextView (Top and Bottom subviews) –SelectionInListView: (Middle subview) Controller: –Controller for each view –Mouse move from subview, activating different views

R R R CSE870: Advanced Software Engineering: Frameworks (Cheng, Sp2003)10 Variations of MVC Framework MacApp (Macintosh applications) Andrew Toolkit (CMU 88) InterViews (Stanford 89) Commercial: –zApp (OS-independent) –OpenStep (part of much bigger, comprehensive system) –Microsoft Foundation Classes

R R R CSE870: Advanced Software Engineering: Frameworks (Cheng, Sp2003)11 Key Principles How to develop successful patterns and frameworks 1.Separate interface from implementation 2.Determine what is Common interface and (common -> stable) Variable implementation 3.Allow substitutions for variable implementations via a common interface Dividing commonality from variability should be goal- oriented rather than exhaustive

R R R CSE870: Advanced Software Engineering: Frameworks (Cheng, Sp2003)12 Open/Closed Principle Determining common vs variable components is important –Insufficient variation makes it hard for users to customize framework components –Insufficient commonality makes it hard for users to understand and depend upon framework’s behavior Generally, dependency should always be in the direction of stability –Component should not depend on any component less stable than itself Open/Closed Principle: –Allows most stable components to be extensible

R R R CSE870: Advanced Software Engineering: Frameworks (Cheng, Sp2003)13 Open/Closed Principle Components should be: –Open for extension –Closed for modification Implications: –Abstraction is good –Inheritance and polymorphism are good –Public data members and global data are bad –Run-time type identification can be bad

R R R CSE870: Advanced Software Engineering: Frameworks (Cheng, Sp2003)14 Violating Open/Closed Principle Struct Shape {/*... */}; Class Square : public Shape { /*... */} Class Circle : public Shape { /*... */} void draw_square {const Square &); void draw_circle {const Circle &); void draw_shape (const Shape &shape) { switch (shape.shapeType) { case SQUARE: draw Square ((const Square &) shape); break; case CIRCLE: draw Circle ((const Square &) shape); break; // etc.

R R R CSE870: Advanced Software Engineering: Frameworks (Cheng, Sp2003)15 Applying Open/Closed Principle class Shape { public: virtual void draw () const = 0; }; void draw all (const Shape &shape){ shape.draw (); }

R R R CSE870: Advanced Software Engineering: Frameworks (Cheng, Sp2003)16 Observations of Frameworks Benefits of frameworks: –Enable direct reuse of code –Enable larger amounts of reuse than standalone functions or individual classes Drawbacks: –High initial learning curve Many classes, many levels of abstraction –Flow of control for reactive dispatching is non- intuitive –Verification/validation of generic components is hard