10/17/2011 Dynamic Semantics Definition of a (programming) language - - PDF document

10/17/2011 1

Generic Language Technology (2IS15)

Dynamic Semantics

• dr. Suzana Andova

Dynamic Semantics

Definition of a (programming) language involves:

• abstract syntax, so-called signature
• concrete syntax:

− textual syntax − graphical syntax

• semantics:

− static semantics − dynamic semantics

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Dynamic Semantics

Semantics represents the intended meaning of a language and language constructs Semantics is a means to represent our understanding of a model/program (what it does) and To communicate our understanding to other entities To understand what happens in a computer/machine when a program/model is executed

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Dynamic Semantics

Not every language is suitable for describing dynamic semantics Dynamic semantics ideally is described in a formal language (formal semantics) because:

− ambiguities and inconsistencies can be detected in a model which appears to be “ok” − this is the basis for analysis, validation and verification, but also implementation

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Dynamic Semantics in practice

• Hardly any modeling language used in industry has formal

semantics

• The semantics of languages is often defined by translation or

interpretation

• Languages evolve and more ambiguities are introduced

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(domain) model (DS) Language (implementation) engine

Dynamic Semantics in practice

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(domain) model (DS) Language (implementation) engine

• Ambiguous representation and

miscommunication

• different understandings of models

Dynamic Semantics in practice

? a c b d e

start-start start-start start-start start-start

how many execution sequences one can think of?  “total” representation required!

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(domain) model (DS) Language (implementation) engine

• Model to implementation inconsistency
• SW constructs do not use semantics, only

syntax

• Code is manually added in the parts

generated

• Cognitive feedback gap between modeling

and model/implementation debugging

• no possibility to transfer results of

execution/debugging back to the original model

• Lack of early design correctness analysis

Dynamic Semantics in practice

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(DSL) model (DS) Language (implementation) engine

• Transformation from one env to another
• Semantic transformation gap
• Model transformation correctness reasoning

Dynamic Semantics in practice

simulation model perform. ana. model test model

transformations

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• Multi-disciplinary project
• Semantic gap between models

Dynamic Semantics in practice

(DSL) model

1

(DS) Language

1

(implementation) engine1

simulation model perform. ana. model test model

transformations

(DSL) model

2

(DS) Language

2

(implementation) engine2

simulation model perform. ana. model test model

transformations

?

• (Reference) Implementation
• Model/program is executed
• Conclusions about the behaviour based
• n observations
• Translational
• Select target language(s)
• Model based in most of the cases
• Interpretation
• Formal semantics
• structural operational semantics (SOS, MSOS)
• denotational semantics
• axiomatic
• algebraic
• game semantics
• …

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Describing Dynamic Semantics

(DSL) model (DS) Language (implementation) engine (Reference) Implementation

• Model/program is executed
• Conclusions about the behaviour based on
• bservations
• if the code is complex (as usual) no behavioural

analysis

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Describing Dynamic Semantics

(DSL) model (DS) Language (implementation) engine

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(DSL) model (DSL) Language (implementation) engine

Model

Target language

engine formal semantics direct translation (properties preservation?)

Describing Dynamic Semantics

Translational semantics

• Model based
• Ad-hoc syntactic mapping
• No semantic mapping -> no

ambiguities detection

• No support for language

evolution

• Inconsistency and Properties

preservation?

• Traceability/reverse mapping

(DSL) model (DSL) Language (implementation) engine

Model

Target language

engine formal semantics direct translation

Describing Dynamic Semantics

Translational semantics

• Ad-hoc semantic mapping
• No semantic mapping -> no

ambiguities detection

• No support for language

evolution

• Inconsistency and Properties

preservation?

• Traceability/reverse mapping

(domain) model DSL (implementation) engine Target model Target language engine

formal semantics formal semantics

design decision? translation for free! correct by construction!

Describing Dynamic Semantics

Formal semantics

• Structural Operational Semantics (SOS, MSOS)

− describes the execution of the program on some (very) abstract machine (G. Plotkin)

• Denotational semantics:

− mathematical definition of input/output relation of the program by induction on its syntactic structure (D. Scott, C. Strachey)

• Axiomatic semantics

− formalization of special properties of the program by logical formulae (assertions and proof rules; R. Floyd, T. Hoare)

• algebraic
• event structures
• ….

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Describing Dynamic Semantics