CASE (Computer-Aided Software Engineering)

Transcription

1 CASE (Computer-Aided Software Engineering) Slide 5.1 Scope of CASE Can support the entire life-cycle Graphical display tools (many for PCs) Data flow diagrams Entity-relationship diagrams Module-interconnection diagrams Petri nets Structure charts

2 Taxonomy of CASE Slide 5.2 UpperCASE versus lowercase Tool versus workbench versus environment

3 Essential Coding Tools Slide 5.3 Coding tools Products (such as text editors, debuggers, and pretty printers) designed to» Simplify programmer s task» Reduce frustration» Increase programmer productivity Conventional coding scenario for programming-in-the-small Editor-compiler cycle Editor-compiler-linker cycle Editor-compiler-linker-execute cycle There must be a better way

4 Graphical Tool Slide 5.4 Additional features Data dictionary Screen and report generators Consistency checker; the various views are always consistent» Specifications and design workbench

5 Syntax-Directed Editor Slide 5.5 Understands language Speeds up implementation User interface of an editor is different to that of a compiler» There is no need to change thinking mode» No mental energy is wasted on these adjustments One piece of system software, two languages» High-level language of module» Editing command language Pretty-printer

6 Online Interface Checker Slide 5.6 Example The programmer tries to call procedure computeaverage, but the linker cannot find it The programmer realizes that the actual name of the procedure is computemean A structure editor must support online interface checking Editor must know name of every procedure Interface checking is an important part of programming-in-the-large

7 Online Interface Checker (contd) Slide 5.7 Example The user enters the call average = computeaverage (dataarray, numberofvalues); Editor immediately responds with a message such as Procedure computeaverage not known Programmer is given two choices Correct the name of the procedure Declare new procedure computeaverage and specify its parameters Enables full interface checking

8 Online Interface Checker (contd) Slide 5.8 Example Declaration of q is void q (float floatvar, int intvar, String s1, String s2); Call (invocation) is q (intvar, floatvar, s1, s2); Online interface checker detects the fault Help facility Online information as to the parameters of method q Better: Editor generates a template for the call» Shows type of each parameter» Programmer replaces formal by actual parameter

9 Online Interface Checker (contd) Slide 5.9 Advantages No need for different tools with different interfaces Hard-to-detect faults are immediately flagged for correction» Wrong number of parameters» Parameters of wrong type Essential when software is produced by a team If one programmer changes the interface specification, all modules calling that changed module must be disabled

10 Online Interface Checker (contd) Slide 5.10 Remaining problem The programmer still has to exit from the editor to invoke the compiler (to generate code) Then, the linker must be called to link the product Must adjust to the JCL, compiler, and linker output

11 Operating System Front-End in Editor Slide 5.11 Single command go or run Use of the mouse to choose icon, or menu selection Causes the editor to invoke the compiler, linker, loader, and execute the product

12 Operating System Front-End in Editor (contd) Slide 5.12 Online documentation Help information regarding» Operating system» Editor» Programming language Programming standards Manuals» Editor manuals» Programming manuals

13 Online Documentation Slide 5.13 Problems with Manuals Updating Essential online documentation Help information Programming standards Manuals

14 Source Level Debugger Slide 5.14 Example: Product executes terminates abruptly and prints Overflow at 4B06, or Core dumped, or Segmentation fault

15 Source Level Debugger (contd) Slide 5.15 The programmer works in a high-level language, but must examine Machine code core dumps Assembler listings Linker listings Similar low-level documentation Destroys the advantage of programming in a high-level language We need Interactive source level debugger (like dbx)

16 Programming Workbench Slide 5.16 Structure editor with Online interface checking capabilities Operating system front-end Online documentation Source level debugger Constitutes a simple programming environment

17 Programming Workbench (contd) Slide 5.17 This is by no means new All the above features are supported by FLOW (1980) The technology has been in place for years Surprisingly, some programmers still implement code Ye Olde-Fashioned Way

18 Software Versions Slide 5.18 During maintenance, at all times there are at least two versions of the product: The old version, and The new version Two types of versions: revisions and variations

19 Revisions and Variations Slide 5.19 Revision Version to fix a fault in the module We cannot throw away an incorrect version Perfective and adaptive maintenance also results in revisions

20 Revisions and Variations (contd) Slide 5.20 Variation Version for different operating system hardware Variations are designed to coexist in parallel

21 Configuration Control Slide 5.21 Every module exists in three forms Source code; object code; executable load image Configuration Version of each module from which a given version of a product is built