FODA expressions

1
FODA expressions

• Pietu Pohjalainen
• MDE ja mallitransformaatiot
• Syksy 2007

2
Feature Oriented Domain Analysis

• FODA is a method for modeling configurability
• Our example is taken from the book Generative
  Programming Methods, Tools, and Applications

3
Dimension

• A feature where all sub features are alternative
• Choose one, but exactly one
• Possible configurations for concept
• f1
• f2
• f3

4
Dimension with optional features

• Feature of which all sub features are alternative
  optional features
• Choose zero, or exactly one
• Possible configurations
• ?
• f1
• f2
• f3

5
Extension point

• Feature that has at least one optional sub
  feature or at least one set of or-sub features
• Possbile configurations
• f2
• f3
• f2, f3
• f1, f2
• f1, f3
• f1, f2, f3

6
Extension point with optional features

• Feature of which all sub features are optional
• Possible configurations
• ?
• f1
• f2
• f3
• f1, f2
• f1, f3
• f2, f3
• f1, f2, f3

7
Extension point with or-features

• Feature of which all direct sub features are
  or-features
• Possible configurations
• f1
• f2
• f3
• f1, f2
• f1, f3
• f2, f3
• f1, f2, f3

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Configuration model for a Car
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Integration to software

• FODA is a simple, yet surprisingly powerful
  approach to modeling variability and
  configurability
• Using a modeling system requires software support
  (IDE, file formats, etc..)
• How does one integrate FODA diagrams to a
  software that is being developed?

10
Approaches to integration

• Build a GUI editor tool for FODA models start an
  internet startup for selling the tool
• Build a text-based DSL (FDL)
• Use existing language (de Jonge Visser)
• Use simpler language (FODA expressions)

11
FODA Description Language FDL

• FDL allows the programmer to express FODA models
  in a text-based form
• Primitives
• all, one-of, more-of
• optional features expressed with ?
• allows also default values

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Car configuration in FDL

• Car
• all(carBody, Transmission, Engine, pullsTrailer?)
• Transmission
• one-of(automatic, manual)
• Engine
• more-of(electric, gasoline)

13
FODA as Context free Grammars

• de Joost and Visser present FODA models as
  context free grammars
• Atomic features are presented as terminals
• Composite features are non-terminals
• Feature operators map to syntax operators
• Allows usage of standard compiler generator tools

14
Car configuration as a CFG

• carBody Transmission Engine pullsTrailer? -gt
  Car
• automatic manual -gt Transmission
• (electric, gasoline) -gt Engine

15
CFG is nice, but too complex?

• CFG approach gives already quite good
  bang-for-buck
• But still some problems
• Implementing CFG requires compiler/parser
  expertise
• Choosing from plethora of tools takes time
• Not always is full expressive power of CFG needed

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FODA Expressions

• Idea use less expressive language
• in FODA expressions, we take the regular
  expressions as the base language
• constraint regexps to match with FODA primitives
• use implementing languages regexp capabilities
• brings e.g. validation close to zero-effort

17
FODA expressions
Dimension (f1 f2 f3)
Dimension with optional features (f1 f2 f3) ?
Extension point (f1? (f2 f3))
Extension point with optional features (f1 f2 f3)
Extension point with or-features (f1 f2 f3)
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Car configuration in FODA expressions

• car body
• transmission (automatic manual)
• engine (electric gasoline)
• pullsTrailer?

19
A DFA to check validity
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Problems with FODA expressions

• To check validity, alphabet in the model need to
  have an order
• Validity checking comes for free, further
  development still requires investment
• E.g. default values, constraints, etc. are not
  expressed
• There might be practical FODA models that are
  really context-free

21
Questions, discussion