1. Strategies for Design & Implementation
of Domain-Specific Languages
From Java to WebDSL and Back
Lecture 5
Course IN4308
Eelco Visser
Master Computer Science
http://eelcovisser.org Delft University of Technology

2. Warning: the code fragments in this
presentation have been grossly
simplified, even when seemingly bulky.
Consult actual code generated by
WebDSL compiler to get the full story.

3. Outline
- Language design strategies
★ inductive vs deductive design
- Compiler architecture
★ compilation by normalization
- WebDSL translation schemes (sketch)
★ entities, templates, access control, validation

4. Design Strategies

5. Designing a Domain-Specific Language
How does one find domain-specific abstractions?
- Deductive (top-down) design
- Inductive (bottom-up) design

6. Deductive (top-down)
- Analyze problem domain
- Identify elements to specify
★ language constructs
- Identify/design solution domain
★ architecture, technology,
- Investigate implementation
★ code generation templates
- Risk
★ design language that is hard to implement

7. Inductive (bottom-up) design
- Consider best practices in solution domain
- Identify coding patterns
- Identify commonality
★ code generation templates
- Identify variability
★ language constructs
- Risk
★ design language that is too low-level

8. Designing a Domain-Specific Language
From JPA/Seam/JSF to WebDSL
- JPA to entity declarations
- JSF to templates
- Seam actions
See CodeGen 2008 slides

9. Compiler Architecture

10. Compiler Architecture
- Syntax
★ check syntactic well-formedness
- Static semantics
★ consistency checking
- Model-to-model transformation
★ desugaring: express constructs in core language
★ add higher-level abstractions
- Code generation
★ translate core language models to implementation

11. Compilation by Normalization

12. Data Model

13. object identity
entity declaration
one-to-many
inverse relation
property

14. Entity Declarations to JPA Entity Classes
- Java Persistence API
- Entity declaration to Java POJO
★ class with private fields, getters, and setters
★ annotations
• values
• relations: one-to-many, many-to-one
★ object identity
- Object-relational mapping
★ entity classes to database tables
★ properties to columns

15. Object Identity
- Automatic identity column for all entities
★ UUID
★ primary key
★ used as foreign key in relations
- Custom symbolic id property
★ key :: String (id)
★ can be changed without compromising foreign keys
★ symbolic id used in URL

16. Entity Class
avoid name clashes
symbolic identity should be unique

17. Object Identity

18. Object Identity
object identity equals primary key

19. Value Type Properties
avoid name clashes

20. Many-to-One Properties
lazy loading
cascading

21. Inverse Properties
update other side of relation

22. HQL Queries

23. Standard Queries

24. Standard Queries

25. Search
- Lucene / Hibernate Search
★ annotations indicate fields to index
- Search queries

26. Generating Hibernate Search Annotations

27. Page Definitions
& Navigation

28. GET | POST
Request URL
Parameters
Client Server
status
Page Response mime type
body

29. page dispatch
parameter passing

30. Pages and Templates to Java Classes

31. Navigate to URL
navigate(topic(t){output(t.name)}
<a href=”/topic/<%t.id%>”> <%t.name%> </a>
<a href=”/topic/FooBar”>FooBar</a>

32. GET | POST name class
Request URL Dispatch topic
Parameters edittopic
page dispatch table
param value
t Foobar
param map
TopicPage
status
Response mime type
serv
body

33. TopicPage.serv

34. TopicPage.serv
request transaction

35. TopicPage.serv
handle request

36. TopicPage.serv
handle request

37. TopicPage.initVarsAndArgs

38. TopicPage.loadArguments

39. TopicPage.loadArguments

40. Render Page

41. Render Page

42. TopicPage.serv
handle post request

43. TopicPage.serv
handle post request

44. class TopicPage extends PageServlet {
serv(request, response, params) {
transaction = newTransaction();
initArguments(params);
if(isPost()) {
storeInputs();
validateInputs();
handleAction();
}
handleExceptions();
render();
storeSessionEntities();
storeMessages();
transaction.commit();
}
}

45. class TopicPage {
render() {
s = templateServlet.render();
response.out(“
<html>
<head>
<%includeCSS()%>
<%includeJS()%>
<%title()%>
</head>
<body>
<%s.write()%>
</body>
</html>
“);
}
}

46. Templates

47. Template Lifecycle
for
each
tem
- Store inputs plat
e
★ bind request parameters to form inputs
- Validate inputs
★ check validation rules
- Handle action
★ execute selected action
- Render
★ print markup
★ render properties of objects

48. ren
der
section nesting
filter special characters

49. ren
der
preventing XSS
rendering WikiText

50. ren
der
parameter passing

51. Forms & Data Binding
form
input
binding
submit
action
issue: bind request parameters to correct binding expressions

52. Data Binding Issues
- Template control-flow
★ template calls: inputs may be nested
★ if-then-else: elements not always present
★ for-loop: multiple occurrences of same form

53. Repeated Form Elements
multiple instances per page

54. Form Abstraction

55. ren
<p>
d er
<label for="input221c5e4216d4669e62bee33efc845eb627">
Title
</label>
<input type="text" value="LoremIpsum" class="inputString"
id="input221c5e4216d4669e62bee33efc845eb627"
name="input231c5e4216d4669e62bee33efc845eb627">
</p>
stor
e inpu
ts

56. ...
ren
d er
<form onsubmit="return clickFirstButton(this);"
method="POST" accept-charset="UTF-8"
action="http://localhost:8080/wiki/editpage2/LoremIpsum"
id="form51c5e4216d4669e62bee33efc845eb627"
name="form51c5e4216d4669e62bee33efc845eb627">
<input type="hidden" value="1"
name="form51c5e4216d4669e62bee33efc845eb627">
<input type="hidden" value="LoremIpsum" name="p">
...
<input type="submit" class="button" value="Save"
name="action61c5e4216d4669e62bee33efc845eb627">
</form>
handle
action
bind action to action code

57. ren
der
<p>
<label for="input241c5e4216d4669e62bee33efc845eb627">
Text
</label>
<textarea id="input241c5e4216d4669e62bee33efc845eb627"
class="inputTextarea inputWikiText"
name="input251c5e4216d4669e62bee33efc845eb627">
value
</textarea>
</p>

58. More Template Issues
- Template calls
★ element parameters
- Nested template definitions
★ closures
- Email templates
★ absolute URLs
- AJAX templates
★ accessible directly from client as page

59. Access Control

60. access control implemented by model-to-model transformation

61. page dispatch takes care of loading & storing session entities

62. More Compilation by Normalization
- Validation
★ validation rules translated to exceptions and
★ see paper
- Workflow
★ workflow procedures & processes
★ translated to functions, access control, user interface

63. Schedule
Lab this week
★ 10 days until deadline Design 1
Cases
★ Case 2: web abstractions
★ See Case 2 for papers to read
Next
★ Lecture 6: language workbenches, modeling
languages
★ Lecture 7: basic code generation