Incremental Change of Software

Transcription

1 Incremental Change of Software

2 Taxonomy of Evolution Changes Incremental change (IC) adds substantial new functionality Refactoring (restructuring) preserves the functionality Replacement substitute one functionality by another example: replacing buggy code Retracting deletes a functionality

3 Strategies for IC Anticipated change information hiding, parametrization localize change within one class Many changes cannot be anticipated process of learning during development Microsoft: 70% of requirements predicted Ford project: 30% predicted examples of unexpected changes company mergers, introduction of Euro

4 Unanticipated IC The Software was not prepared/designed for it Very common situation in practice A substantial part of software engineering

5 Initiation The Mini-process of IC IC design IC implementation & Tests Release

6 IC Initiation Problem Report May require logs, traces Preventive Maintenance enhance reliability, comprehensibility, extensibility, etc. New Feature Request additional functionality of the product usually initiated by the customers, marketing, management All change requests assigned a priority and placed on the queue hot problems cause instant reprioritization

7 IC Design Concept Location Find where in the code the change will be done Study Code and Documentation Identify/Weigh Alternative Solutions Implementation strategy Divide large changes into several smaller ones Each has its own implementation and testing activity Impact analysis Find all components that will be affected by the change

8 IC Implementation Refactoring 1 (pre-factoring) Restructure the software to localize change Actualization Implements the new code Incorporation Replaces the new code by the old Change propagation Changes all other components that must be changed Refactoring 2 (post-factoring) Improves clarity, readability

9 Testing Unit tests of the components Guarantee that units (classes) work Regression test Guarantee that things that did not change still work Integration test Guarantee that the whole system works again Tests are done both during and after implementation

10 IC Release Release build Write Release Notes Make release available to customer

11 Concept location plays key role in IC concepts are present in the code primitive concepts have to be enriched Point-of-Sale: introduce credit card payment old code: payment represented as just one number latent concepts have to be implemented Student Registration: introduce prerequisite check old code assumption: prerequisites are satisfied

12 Concept location finds code that implements concept part of program comprehension concept location methodologies human knowledge "grep" (pattern matching) dynamic search (execution traces) static search through dependency graph traceability tools

13 Top-down search Depth first search done by programmer: Start with the top class (main in C++) while (concept is not implemented here) if (the concept is a part of the composite functionality) move to subclass which leads to the concept else backtrack concept located

14 Change propagation Refactoring 1 (pre-factoring) Restructure the software to localize change Actualization Implements the new code Incorporation Replaces the new code by the old Change propagation Changes all other components that must be changed Refactoring 2 (post-factoring) Improves clarity, readability

15 Change propagation if the visited class is modified, it may no longer fit secondary changes must be made in interacting ( neighboring ) classes secondary changes may trigger additional changes ripple effect Process Mark neighboring classes of a class that changed visit the marked classes one-by-one

16 Three possibilities for marked Change class Mark all neighbors class visit Do not change class but propagate Mark all neighbors Do not change class and do not propagate Erase the mark

17 Three options (class diagram) Change class mark Do not change class but propagate

18 Three options (class diagram) Do not change class and do not propagate

19 Example change propagation Point-Of-Sale application Old program keeps an inventory, receives delivery, sells products, and supports a cash register. Classes designed and implemented at a minimal level of functionality

20 UML class diagram

21 Incremental change complexities of sale taxes different products may have different sales tax, depending on state law location tax in class item actualization new class taxcategory

22 Incorporation register store item sale salelineitem taxcategory

23 Change propagation register store item sale salelineitem taxcategory

24 Change propagation register store item sale salelineitem taxcategory

25 Change propagation register store item sale salelineitem taxcategory

26 Change propagation register store item sale salelineitem taxcategory

27 Change propagation register store item sale salelineitem taxcategory

28 Summary adding tax 1 new class was implemented All 5 old classes had to be visited (!) 3 old classes had to be changed

29 Example Drawlets Application framework Drawlets adds graphical display to a host application Drawing canvas lines, free-hand lines, rectangles, rounded rectangles, triangles, pentagons, polygons, ellipses, text boxes, images

30 Drawlets more than 100 classes, 35 interfaces and 40,000 lines of code originally implemented by Kent Beck, Ward Cunningham later ported into Java perfect API drawlets.htm

31 The host application responsible for providing an instance of the drawing canvas, toolbars, and tool buttons Class SimpleApplet is a host application is a part of the Drawlet library SimpleApplet runs in any browser

32 SimpleApplet window

33 Top classes LocatorConnectionHandle Locator AbstractFigure Figure StylePalette SequenceOfFigures SimpleApplet DrawingCanvas ToolBar CanvasTool SimpleDrawingCanvas ToolPalette SelectionTool ConstructionTool PrototypeConstructionTool ShapeTool LabelTool RectangleTool EllipseTool RectangularCreationTool PG_RectImageTool

34 Concept Location :: Example Locating figure properties in Drawlets

35 Example Drawlets: Top class LocatorConnectionHandle Locator AbstractFigure Figure StylePalette SequenceOfFigures SimpleApplet DrawingCanvas ToolBar CanvasTool SimpleDrawingCanvas ToolPalette SelectionTool ConstructionTool PrototypeConstructionTool ShapeTool LabelTool RectangleTool EllipseTool RectangularCreationTool PG_RectImageTool

36 Wrong way LocatorConnectionHandle Locator AbstractFigure Figure StylePalette SequenceOfFigures SimpleApplet DrawingCanvas ToolBar CanvasTool SimpleDrawingCanvas ToolPalette SelectionTool ConstructionTool PrototypeConstructionTool ShapeTool LabelTool RectangleTool EllipseTool RectangularCreationTool PG_RectImageTool

37 Backtrack LocatorConnectionHandle Locator AbstractFigure Figure StylePalette SequenceOfFigures SimpleApplet DrawingCanvas ToolBar CanvasTool SimpleDrawingCanvas ToolPalette SelectionTool ConstructionTool PrototypeConstructionTool ShapeTool LabelTool RectangleTool EllipseTool RectangularCreationTool PG_RectImageTool

38 Right way LocatorConnectionHandle Locator AbstractFigure Figure StylePalette SequenceOfFigures SimpleApplet DrawingCanvas ToolBar CanvasTool SimpleDrawingCanvas ToolPalette SelectionTool ConstructionTool PrototypeConstructionTool ShapeTool LabelTool RectangleTool EllipseTool RectangularCreationTool PG_RectImageTool

39 Wrong way LocatorConnectionHandle Locator AbstractFigure Figure StylePalette SequenceOfFigures SimpleApplet DrawingCanvas ToolBar CanvasTool SimpleDrawingCanvas ToolPalette SelectionTool ConstructionTool PrototypeConstructionTool ShapeTool LabelTool RectangleTool EllipseTool RectangularCreationTool PG_RectImageTool

40 Backtrack LocatorConnectionHandle Locator AbstractFigure Figure StylePalette SequenceOfFigures SimpleApplet DrawingCanvas ToolBar CanvasTool SimpleDrawingCanvas ToolPalette SelectionTool ConstructionTool PrototypeConstructionTool ShapeTool LabelTool RectangleTool EllipseTool RectangularCreationTool PG_RectImageTool

41 Concept Location :: Summary LocatorConnectionHandle Locator AbstractFigure Figure StylePalette SequenceOfFigures SimpleApplet DrawingCanvas ToolBar CanvasTool SimpleDrawingCanvas ToolPalette SelectionTool ConstructionTool PrototypeConstructionTool ShapeTool LabelTool RectangleTool EllipseTool RectangularCreationTool PG_RectImageTool

42 Change Request implement an "owner" for each figure owner put that figure onto the canvas only owner is allowed to move that figure each session declares a session owner this session owner will own all new figures created no other owner will be allowed to manipulate them This change will make SimpleApplet more versatile and useful support for cooperative work

43 Extraction The concepts relevant to the change figure owner and session owner both are implicit old code assumes that there is just one owner who owns both sessions and figures

44 Location LocatorConnectionHandle Locator AbstractFigure Figure StylePalette SequenceOfFigures SimpleApplet DrawingCanvas ToolBar CanvasTool SimpleDrawingCanvas ToolPalette SelectionTool ConstructionTool PrototypeConstructionTool ShapeTool LabelTool RectangleTool EllipseTool RectangularCreationTool PG_RectImageTool

45 Actualization LocatorConnectionHandle Locator AbstractFigure Figure StylePalette SequenceOfFigures OwnerIdentity SimpleApplet DrawingCanvas ToolBar CanvasTool SimpleDrawingCanvas SimpleListener ToolPalette SelectionTool ConstructionTool PrototypeConstructionTool ShapeTool LabelTool RectangleTool EllipseTool RectangularCreationTool PG_RectImageTool

46 Incorporation LocatorConnectionHandle Locator AbstractFigure Figure StylePalette SequenceOfFigures OwnerIdentity SimpleApplet DrawingCanvas ToolBar CanvasTool SimpleDrawingCanvas SimpleListener ToolPalette SelectionTool ConstructionTool PrototypeConstructionTool ShapeTool LabelTool RectangleTool EllipseTool RectangularCreationTool PG_RectImageTool

47 Propagation LocatorConnectionHandle Locator AbstractFigure Figure StylePalette SequenceOfFigures OwnerIdentity SimpleApplet DrawingCanvas ToolBar CanvasTool SimpleDrawingCanvas SimpleListener ToolPalette SelectionTool ConstructionTool PrototypeConstructionTool ShapeTool LabelTool RectangleTool EllipseTool RectangularCreationTool PG_RectImageTool

48 Propagation LocatorConnectionHandle Locator AbstractFigure Figure StylePalette SequenceOfFigures OwnerIdentity SimpleApplet DrawingCanvas ToolBar CanvasTool SimpleDrawingCanvas SimpleListener ToolPalette SelectionTool ConstructionTool PrototypeConstructionTool ShapeTool LabelTool RectangleTool EllipseTool RectangularCreationTool PG_RectImageTool

49 Propagation LocatorConnectionHandle Locator AbstractFigure Figure StylePalette SequenceOfFigures OwnerIdentity SimpleApplet DrawingCanvas ToolBar CanvasTool SimpleDrawingCanvas SimpleListener ToolPalette SelectionTool ConstructionTool PrototypeConstructionTool ShapeTool LabelTool RectangleTool EllipseTool RectangularCreationTool PG_RectImageTool

50 Propagation LocatorConnectionHandle Locator AbstractFigure Figure StylePalette SequenceOfFigures OwnerIdentity SimpleApplet DrawingCanvas ToolBar CanvasTool SimpleDrawingCanvas SimpleListener ToolPalette SelectionTool ConstructionTool PrototypeConstructionTool ShapeTool LabelTool RectangleTool EllipseTool RectangularCreationTool PG_RectImageTool

51 Propagation LocatorConnectionHandle Locator AbstractFigure Figure StylePalette SequenceOfFigures OwnerIdentity SimpleApplet DrawingCanvas ToolBar CanvasTool SimpleDrawingCanvas SimpleListener ToolPalette SelectionTool ConstructionTool PrototypeConstructionTool ShapeTool LabelTool RectangleTool EllipseTool RectangularCreationTool PG_RectImageTool

52 Propagation LocatorConnectionHandle Locator AbstractFigure Figure StylePalette SequenceOfFigures OwnerIdentity SimpleApplet DrawingCanvas ToolBar CanvasTool SimpleDrawingCanvas SimpleListener ToolPalette SelectionTool ConstructionTool PrototypeConstructionTool ShapeTool LabelTool RectangleTool EllipseTool RectangularCreationTool PG_RectImageTool

53 Propagation LocatorConnectionHandle Locator AbstractFigure Figure StylePalette SequenceOfFigures OwnerIdentity SimpleApplet DrawingCanvas ToolBar CanvasTool SimpleDrawingCanvas SimpleListener ToolPalette SelectionTool ConstructionTool PrototypeConstructionTool ShapeTool LabelTool RectangleTool EllipseTool RectangularCreationTool PG_RectImageTool

54 Shorter change propagation Long change propagation is a problem it would be advantageous to shorten it opportunistic refactoring moves code affected by change into fewer classes splitting the roles

55 More info on the case study Václav Rajlich, Prashant Gosavi: Incremental Change in Object-Oriented Programming. IEEE Software 21(4): (2004)