1 TRANSFORM ANALYSIS Heuristics and Rules

2 DFD with Transform Flow Characteristics input-driven output-driven center of transformation

3 Structured Analysis and Design Information Flow Analysis 1 - specify the flow of information in your system => DFD 2 - identify typical structural patterns in the DFD => analysed & annotated DFD 3 - use a proven heuristic to map DFD into SC => first SC 4 - refine and check your Structure Chart => final SC

4 Structured Analysis and Design Transform Analysis 1 - specify the flow of information in your system 2 - a) confirm transform flow characteristics b) identify the center of transformation ===> annotated DFD 3 - transform your DFD into a first Structure Chart using IPO structure as design heuristic 4 - refine and check your Structure Chart ===> complete SC

5 Transform Analysis - Step 1 the DFD should exist as a result of systems requirements engineering and systems analysis check completeness of the DFD, data dictionary, and process dictionary refine the DFD (decompose, etc.) if that is necessary

6 registration read & check reg. prepare invoice accept reg. print invoice write conf. user printer registration db reg+ reg_info conf. invoice reg- profile prices invoice_prt conf_msg error_msg

7 read registration check registration error-handler registration reg+ error_reason error_msg reg_i

8 Transform Analysis - Step 2 Step 2a: –check the list of properties for transform flow characteristics –be aware that this is a guideline only Step 2b: –find and mark the center of transformation in the DFD

9 Transform Analysis - Step 2b locate the center of transformation –follow input-driven flows into the center until the data is in an internal format, correct and complete ===> mark position –trace back output-driven flows to the center until the data is complete and ready for presentation, but not yet in external format ===> mark position connect all markings: center of transformation

10 registration read & check reg. prepare invoice accept reg. print invoice write conf. user printer registration db reg+ reg_info conf. invoice reg- profile prices invoice_prt conf_msg error_msg center of transformation

11 read registration check registration error-handler registration reg+ error_reason error_msg reg_i

12 Transform Analysis - Step 3 IPO mapping heuristic i1 i2 ct1 ct2 o1o2 o3 sys I-ctrlP-crtlO-ctrl i1i2ct1ct2o1o2o3

13 The IPO Mapping & Design Heuristic establish a top level main controller (system) always introduce: –Input-driven flow controller –transform flow controller (Processing) –Output-driven flow controller translate DFD processes into SC modules and hang them from the correct controller allocate subprocesses => submodules

14 reg. sys. read & check comp reg. prod. output read reg. check reg. error hdlg. reg. prep. inv. acc. reg. print inv. write conf. crtdbprtcrt

15 Transform Analysis - Step 4 add data (and control) flows further decompose (factor) were necessary –user interface handling modules –error-handling modules –add initialisation & termination modules check quality of design: –cohesion –coupling reconfirm mapping with DFD

16 See our Structure Chart Example (Section 3c) for a complete specification of data and control flows.

17 End of Section 3e coming up: software design quality