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When and How to Develop
Domain-Specific Languages
CMP586 – Trends in Software Engineering
Presenter: Vítor De Araújo
About the article
Authors
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Marjan Mernik
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Jan Heering
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CWI, Netherlands
Anthony M. Sloane
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University of Maribor, Slovenia
Macquarie University, Australia
Published in 2005
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About the article
Organization
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Section 1: Introduction
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Section 2: DSL patterns
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Common patterns in the creation of DSLs
Section 3: DSL development support
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Characterizes DSLs and what they are good for
Tools for helping in design and implementation of DSLs
Section 4: Conclusion and open problems
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Section 1. Introduction
General
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DSLs trade generality for expressiveness in a limited domain
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Expressiveness, maintenance costs
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Opens up development to larger group of developers (domain
experts)
Hard to quantify the productivity gains of using DSLs
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Has been done for specific DSLs before
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In this article we will keep to qualitative analysis
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Application domain: vague concept
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Contrast to application libraries
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notations, better abstractions, analysis/optimization
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however, libraries are often more cost-effective
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Section 1. Introduction
Executability of DSLs
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DSLs are executable to varying extents
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Excel, HTML > app. generator > BNF > Non-executable
Some references don't consider non-executable languages as
DSLs
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Section 1. Introduction
DSLs as enablers of reuse
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Many reusable artifacts
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Language grammars
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Source code
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Domain abstractions
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Software designs
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Notations used by domain experts
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Section 1. Introduction
Scope of this article
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DSL development does not come for free
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Requires both domain and language development expertise
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More variation than found in GPLs
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Training material, standardization, support, maintenance
Need of a DSL may become clear only after large portion of
software was written
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Software reengineering / evolution
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Section 2. DSL patterns
Pattern classification
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Phases of DSL development
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Decision (perhaps we need a DSL)
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Analysis (identify domain, collect domain knowledge)
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Design (how will the concepts be expressed in language)
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Implementation (exactly what it sounds like)
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Deployment (out of the scope of this article)
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Not necessarily a sequential process
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Common patterns in each of these phases
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Section 2. DSL patterns
Decision
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Does it pay to develop a DSL?
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Short-term considerations, lack of expertise → postponement
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Using existing DSL may be easier
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But hard to find available suitable DSLs
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Adapting unknown DSL may be considered too risky
General concerns which lead to decision for DSL
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improved software economics
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Enabling development by users with less programming
expertise
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Section 2. DSL patterns
Decision: common motivational patterns
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Notation (new or existing)
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Transform visual to textual notation
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User-friendly notation to existing API
AVOPT (Analysis, Verification, Optimization, Parallelism,
Transformation)
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Often overlaps with other patterns
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Task automation
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Product line (share common architecture)
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Data structure definition and traversal
Interaction
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When menus are not flexible enough
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Section 2. DSL patterns
Analysis
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Domain is identified and domain knowledge gathered
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Input from various sources
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Domain experts
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Technical documents
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Existing general-purpose-language code
Output
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Terminology and semantics in abstract form
Link with knowledge engineering
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Section 2. DSL patterns
Analysis
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Most often informal
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Sometimes domain analysis methodologies are used
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DARE, DSSA, FAST, FODA, etc.
Formal analysis produces a domain model
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Domain definition (scope)
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Domain terminology (vocabulary, ontology)
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Descriptions of domain concepts
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Feature models (commonalities, variabilities, dependencies)
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Section 2. DSL patterns
Analysis
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Analysis → DSL: no clear guidelines, but we have some:
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Variabilities: information to specify an instance of the system
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Commonalities: execution model and primitives
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Terminology and concepts: DSL constructions
On the basis of a single domain analysis, many DSLs may be
developed
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But all share important characteristics found in the feature
model
An introduction to FODA and FAST follows (which we'll skip)
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Section 2. DSL patterns
Design
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Approaches can be characterized along two dimensions
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Relationship between DSL an existing languages
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Language exploitation
● Language invention
Formality of the design description
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Informal
● Formal
(and everything in between)
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Section 2. DSL patterns
Design: with respect to existing languages
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Easiest to base the DSL on an existing language
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Easier to implement
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Easier to learn (assuming users know the existing language)
Three patterns
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Piggyback
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Specialization
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Extension
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Section 2. DSL patterns
Design: with respect to existing languages
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Alternatively, we can do it from scratch
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Can be extremely difficult and hard to characterize
One must keep in mind the special character of DSLs
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Not your run-of-the-mill general-purpose language
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Users are not necessarily programmers
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Adopt notations/concepts from domain, rather than trying to
"improve" them (e.g., over-generalize)
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Design only what is necessary
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Section 2. DSL patterns
Design: with respect to formality
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Informal design
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Natural language, examples of illustrative DSL programs
Formal design
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Syntax:
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regular expressions
● grammars
Semantics:
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attribute grammars
rewrite systems
abstract state machines
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Section 2. DSL patterns
Design: with respect to formality
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Informal design is probably easier for most people
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But some formality can go a long way
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Highlight problems before implementation
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Implementation may be partially automated
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e.g., parser generators
Often:
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Language invention ~ formal design
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Language exploitation ~ informal design
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Section 2. DSL patterns
Implementation
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Some DSL-specific techniques have no useful counterpart in
GPLs
Patterns
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Interpreter
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Compiler / application generator
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Preprocessor (macros, source-to-source)
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Embedding
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Extensible compiler/interpreter
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Commercial Off-The-Shelf (COTS)
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Hybrid
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Section 2. DSL patterns
Implementation: trade-offs
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Interpreter/compiler
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Full syntactic flexibility (closer to domain notations)
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Good error reporting is possible
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AVOPT is possible
On the other hand...
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Requires more effort
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Design from scratch: greater risk of incoherent design
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Section 2. DSL patterns
Implementation: trade-offs
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Embedding
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Requires less effort
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Language is often more powerful because host language
constructs are available
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Easier to learn for users familiar with the host language
On the other hand...
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Syntax is not optimal (constrained by host language)
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Overloading may lead to confusion
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Bad error reporting (host-language rather than DSL-specific)
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Section 3. DSL development support
Design and implementation support
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Language development systems/toolkit
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Generated tools may vary
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Consistency checker and interpreter
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Full-blown IDE with syntax-directed editor, analysis, etc.
Even non-executable languages may benefit from tools
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Generate tools from language descriptions
e.g., syntax-directed editor, pretty-printing, checking
Some tools are methodology-agnostic, some require specific
methodology
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Section 3. DSL development support
Analysis support
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Separate frameworks and tools for domain analysis
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Collaborative development of semantic models
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Capture of domain information from experts
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Structured editors and hypertext/media engine
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Ontology editors
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etc.
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Section 4. Conclusions and open problems
Conclusions
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DSLs will never be a solution to all sw. engineering problems
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However, currently application unduly limited by lack of
knowledge available to potential DSL developers
We distinguish 5 phases of DSL development
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decision, analysis, design, implementation, [deployment]
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We identify patterns to help guide this process
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We have seen toolkits to help in DSL development
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However, there are gaps which could use further work
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Section 4. Conclusions and open problems
Open problems
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Decision: Can be aided by computers?
Analysis: Integration between domain analysis tools and DSL
design/implementation tools
Design and implementation: Can be made easier for people not
versed in language development? E.g.:
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building blocks for DSL construction
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combining existing GPLs and DSLs
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pattern-aware development support
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description by example
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Embedding: More support from GPLs
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Estimation: Can we quantify costs and benefits of DSLs?
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Thanks.
Questions?
Vítor De Araújo
vbuaraujo@inf.ufrgs.br