Abstractness, Specificity, and Complexity in Software Design

Transcription

1 Abstractness, Specificity, and Complexity in Software Design Stefan Wagner and Florian Deißenböck Technische Universität München, Germany Florian Deißenböck ROA, Fakultät für Informatik Lehrstuhl für Software & Systems Engineering

2 Abstraction Examples C Assembler Microcode CPU

3 Abstraction Examples Simulink C Assembler Microcode CPU

4 Abstraction Examples Simulink BPEL C Assembler Microcode CPU

5 Abstraction Examples Simulink BPEL C Web Service Framework Assembler HTTP Library Microcode Networking Library CPU Network Adapter

6 Abstraction Examples Simulink BPEL C Web Service Framework GUI Builder Assembler HTTP Library GUI Framework Microcode Networking Library Operating System CPU Network Adapter Graphics Adapter

7 Abstraction Examples Simulink BPEL Persistence Framework C Web Service Framework GUI Builder SQL Assembler HTTP Library GUI Framework B-Tree Microcode Networking Library Operating System Database CPU Network Adapter Graphics Adapter

8 Abstraction Examples Business Application Construction Kit Simulink BPEL Persistence Framework C Web Service Framework GUI Builder SQL Assembler HTTP Library GUI Framework B-Tree Microcode Networking Library Operating System Database CPU Network Adapter Graphics Adapter

9 Abstraction Examples Business Application Construction Kit Simulink BPEL Persistence Framework C Web Service Framework GUI Builder SQL Assembler HTTP Library GUI Framework B-Tree Microcode Networking Library Operating System Database CPU Network Adapter Graphics Adapter

10 Abstraction Examples Business Application Construction Kit Simulink C Assembler Microcode BPEL An abstraction for a software artifact is a succinct Web Service description that GUI suppresses Builder the Framework details that are unimportant to a software developer and emphasizes the information that is important. HTTP Library Networking Library GUI Framework C. W. Krueger Operating System Persistence Framework SQL B-Tree Database CPU Network Adapter Graphics Adapter

11 Problem Statement Abstraction is of paramount importance for software development. Simulink BPEL What are the implications on specificity? What are the implications on complexity? What are the implications and trade-offs in abstractions? How to design and use abstractions? C Assembler Microcode CPU

12 Two Levels of Abstraction Variable Abstraction Specification Vn Vn-1 V2 V1 Abstraction Realization [C. W. Krueger. Software Reuse. 1992]

13 Two Levels of Abstraction Variable Abstraction Specification Vn Abstraction Realization Vn-1 Example public JFrame createwindow(string title) { JFrame frame = new JFrame(title); V2 frame.setcloseop(exit_on_close); V1 frame.pack(); frame.setvisible(true); return frame; } [C. W. Krueger. Software Reuse. 1992]

14 Abstractness & Specificity Abstractness Abstraction means information loss Remove explicit detail model building Defined by amount of variable information Specificity Defined by the number of contexts it can be used in The larger the variable part, the more generic The larger the fixed part, the more specific generic specific Variable

15 Complexity Complexity reduction is a main goal of abstraction Various definitions (even philosophy has not a unique one) Detail complexity*: Number of parts Dynamic complexity*: Cause and effect relationships Detail Complexity Dynamic Complexity * [Peter M. Senge. The Fifth Discipline. 1990]

16 Types of Abstraction C1 t1 C2 t2

17 Types of Abstraction C1 t1 JFrame f = new JFrame( Choose Target File ); JFrame f = new JFrame( Choose Source File ); f.setcloseop(exit_on_close); f.setcloseop(exit_on_close); C2 t2

18 Types of Abstraction Cg p:t C1 t1 JFrame f = new JFrame( Choose Target File ); JFrame f = new JFrame( Choose Source File ); f.setcloseop(exit_on_close); f.setcloseop(exit_on_close); C2 t2

19 Types of Abstraction Cg p:t public JFrame createwindow(string title) { } C1 t1 JFrame f = new JFrame( Choose Target File ); JFrame f = new JFrame( Choose Source File ); f.setcloseop(exit_on_close); f.setcloseop(exit_on_close); C2 t2

20 Types of Abstraction Cg p:t public JFrame createwindow(string title) { } Generalizing Abstraction C1 t1 JFrame f = new JFrame( Choose Target File ); JFrame f = new JFrame( Choose Source File ); f.setcloseop(exit_on_close); f.setcloseop(exit_on_close); C2 t2

21 Types of Abstraction C t Cg p:t public JFrame createwindow(string title) { } Generalizing Abstraction C1 t1 JFrame f = new JFrame( Choose Target File ); JFrame f = new JFrame( Choose Source File ); f.setcloseop(exit_on_close); f.setcloseop(exit_on_close); C2 t2

22 Types of Abstraction C t public JFrame createfilewindow() { return createwindow( Choose File ); } Cg p:t public JFrame createwindow(string title) { } Generalizing Abstraction C1 t1 JFrame f = new JFrame( Choose Target File ); JFrame f = new JFrame( Choose Source File ); f.setcloseop(exit_on_close); f.setcloseop(exit_on_close); C2 t2

23 Types of Abstraction C t public JFrame createfilewindow() { return createwindow( Choose File ); } Simplifying Abstraction Cg p:t public JFrame createwindow(string title) { } Generalizing Abstraction C1 t1 JFrame f = new JFrame( Choose Target File ); JFrame f = new JFrame( Choose Source File ); f.setcloseop(exit_on_close); f.setcloseop(exit_on_close); C2 t2

24 The Influences of Abstraction Type Specificity Detail Complexity Dynamic Complexity Simplifying Abstraction Generalizing - 0/- + Simplifying + - +/- t1 p:t Generalizing Abstraction t2

25 Consequences 1. Generalizing abstraction increases dynamic complexity 2. Simplifying abstraction increases specificity 3. To manage complexity, design specific and generic

26 Consequences 1. Generalizing abstraction increases dynamic complexity 2. Simplifying abstraction increases specificity 3. To manage complexity, design specific and generic Example Swing JFrame can be used by setting only one of its > 65 parameters.

27 Conclusions Motivation Abstraction is an essential activity in software engineering Used to increase comprehensibility and reuse Effects are rarely discussed and not well understood Contribution Two basic types of abstraction: simplifying and generalizing Influences on specificity and complexity Future work Developing more examples Formal framework Relation to redundancy?