Understanding Legacy Systems

1
Understanding Legacy Systems

• Arie van Deursen
• Tobias Kuipers
• Leon Moonen

2
Tooling Infrastructure
Lexical Analysis
Report Generator
Legacy Sources
Repository
Syntax Analysis
Cluster Analysis
Data flow Analysis
Visuali- zation
Filter Abstract
3
Redocumentation

• Contents decided by maintenance team.
• Technical system knowledge lost!
• Automatic extraction
• Manual additional docs, overviews
• Training, changes, estimates, ...

4
Understanding Variables

• 100 Kloc Cobol
• 25,000 different variables!
• Cobol variable declarations
• Aggregation byte representation
• No types!

5
Type Inference for COBOL

• Give each variable unique primitive type
• Infer type-equiv. and subtype relations
• x y, x y, x y, literals, ...
• DB operations, calls, copybooks
• Partial order of equivalence classes

OCallahan 97 C Henglein 99 Y2K WCRE98,
IWPC99
6
Applications

• Y2K Euro
• Constant (de)propagation
• Program-level documentation
• System-level signatures
• Language migrations
• Object identification

7
Object Identification

• Legacy data structures
• attributes
• Legacy functionality
• methods

Select Domain Concepts
Combination Candidate classes!
Persistent data types Progrs low fan in/out
8
Concept Analysis

• Concept (I, F )
• maximal set of items I ? I
• sharing set of features F ? F
• From feature table T ? I ?F
• generate all concepts
• Lattice (I1, F1) ? (I2, F2 ) ? I1 ? I2

Siff/Reps97 Lindig/Snelting97 IWPC98, ICSE99
9

Many fields
Progr. nrs
Concept
Fields
One field
10
System Understanding

• Analysis of legacy sources
• Select good parts
• Filter out hopeless elements
• Combine present in novel ways
• Tool support rather than automation