Developers in modern general-purpose programming languages create reusable code libraries by encapsulating them in Applications Programming Interfaces (APIs). Domain-specific languages (DSLs) can be developed as an alternative method for code abstraction and distribution, sometimes preferable to APIs because of their expressivity and tailored development environment. However the cost of implementing a fully functional development environment for a DSL is generally higher. In this paper we propose DSLit, a prototype-tool that, given an existing API, reduces the cost of developing a corresponding DSL by analyzing the API, automatically generating a semantically equivalent DSL with its complete development environment, and allowing for user customization. To build this bridge between the API and DSL technical spaces we make use of existing Model-Driven Engineering (MDE) techniques, further promoting the vision of MDE as a unifying technical space.

1. Valerio Cosentino
Massimo Tisi
Javier Luis Canovas Izquierdo
SOFSEM, 2015, Pec pod Sněžkou, Czech Republic
A Model-Driven Approach to Generate
External DSLs from Object-Oriented
APIs
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2. Outline
 Introduction
 Model Driven Engineering
 From API to DSL
 Conclusion and Future work
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3. Introduction
 Code abstraction and reuse allow the use of
existing software knowledge (i.e., code
libraries) to build new software by reducing:
– Time
– Resources
– Redundancy
 Code libraries can be accessed via:
– APIs using mechanisms (function call, class
inheritance, etc.) provided by the General-
purpose Programming Language (GPL)
– DSLs (Domain Specific Languages)
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4. Introduction
 API vs DSL:
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5. Introduction
 Are DSLs better than APIs?[1]
– Pros:
 DSLs can be more expressive,
maintainable, concise and readable
 Static validation, syntax highlighting, etc.
 Interpretation/compilation optimized for
the DSL code execution
– Cons:
 DSLs requires a higher development
cost
[1] Kelly, S., Tolvanen, J.P.: Domain-Specific Modeling: Enabling Full Code
Generation. Wiley IEEE Computer (2008)
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6. Introduction
 How to reduce the development cost when
building a DSL?
– Model Driven Engineering (MDE)
 Automatic generation of DSL
components:
– compiler, validator, development
environment
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7. Model Driven Engineering
 What is MDE?
– Models: first class entities in MDE (abstract
representation of the knowledge for a given domain)
– Model transformations: operaration for model handling
 Injectors/extractors to move between technical spaces [2]
[2] Kurtev, I., Bezivin, J., Aksit, M.: Technological Spaces : an Initial
Appraisal. In: DOA. (2002) 1–6
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8. From API to DSL
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9. From API to DSL
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10. From API to DSL
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11. API classes to API metamodel
 Mapping[3]
– API class definitions  metamodel elements
– Java classes  metaclasses
 Attributes  metaclass attributes
 Methods  operations
 Customization:
– Some APIs can generate very large
metamodels
 Selection of a subset of API elements
– Tunable API metamodel
 Manual modifications
[3] Canovas Izquierdo, J.L., Jouault, F., Cabot, J., Garcıa Molina, J.:
API2MoL: Automating the building of bridges between APIs and Model-
Driven Engineering. Inform. Software Tech. 54(0) (2012) 257–273
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12. From API to DSL
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13. API metamodel to DSL metamodel
 Domain-specific concepts extracted from the
API metamodel
 Domain-independent API structure
– Templates
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14. Templates
 Plain Old Data (POD)
– For simple APIs to create and maintain a
data structure
– API classes composed by getters, setters
and constructors
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15. Templates
 Fluent
– For APIs that rely on chaining method calls
– The return values of the method calls
(keywords) are used to structure the DSL
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16. Templates
 SimpleJava
– For APIs that do not fit in the previous
categories
– Java sub-set(statements, declarations, etc.)
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17. From API to DSL
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18. DSL metamodel to DSL tooling
 Bridge between the Model TS and the Grammar TS
– Mapping of metamodel elements into the grammar
rules
– Development environment
 The generation process is parameterized by:
– The DSL metamodel (concepts, attributes,
references, cardinalities, etc.)
– The template chosen (the grammar structure, the
development environment and compiler)
– Particularized for Xtext[4]
[4] Eysholdt, M., Behrens, H.: Xtext: implement your language faster than
the quick and dirty way. In: SPLASH. (2010) 307–309
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19. From API to DSL
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20. Compiler generation
 Since the semantics of the DSL template is
known, a DSL instance can be transformed
into its equivalent in Java
– SimpleJava
 DSL concepts have a one-to-one
correspondence with Java constructs
 DSL model to Java model (MoDisco[5])
 Java model to Java readable file (Acceleo[6])
[5] http://www.eclipse.org/gmt/modisco/technologies/J2SE5/
|6] http://www.eclipse.org/acceleo
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21. Conclusion and Future work
 MDE approach to connect API, Model and Grammar
technical spaces
 Template mechanism to generate the resulting DSL
 Proof of concept
 Future work:
– Identify more templates to cover other types of
DSLs (API characterization)
– Study how our method could cope with more
complex APIs (event-driven, concurrent, etc.)
– Explore how distinct APIs used in the same GPL can
be combined at DSL-level (interleaving DSLs)
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