Strategies for Design & Implementation of Domain-Specific Languages

From Java to WebDSL and Back

Course IN4308Master Computer Science

Delft University of Technology

Eelco Visserhttp://eelcovisser.org

Lecture 5

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.

Outline

- Language design strategies

★ inductive vs deductive design

- Compiler architecture

★ compilation by normalization

- WebDSL translation schemes (sketch)

★ entities, templates, access control, validation

Design Strategies

Designing a Domain-Specific Language

How does one find domain-specific abstractions?

- Deductive (top-down) design

- Inductive (bottom-up) design

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

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

Designing a Domain-Specific Language

From JPA/Seam/JSF to WebDSL

- JPA to entity declarations

- JSF to templates

- Seam actions

See CodeGen 2008 slides

Compiler Architecture

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

Compilation by Normalization

Data Model

object identity

inverse relation

entity declaration

one-to-many

property

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

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

Entity Class

avoid name clashes

symbolic identity should be unique

Object Identity

Object Identity

object identity equals primary key

Value Type Properties

avoid name clashes

Many-to-One Properties

cascading

lazy loading

Inverse Properties

update other side of relation

HQL Queries

Standard Queries

Standard Queries

Search

- Lucene / Hibernate Search

★ annotations indicate fields to index

- Search queries

Generating Hibernate Search Annotations

Page Definitions & Navigation

Server

Request URL

GET | POST

Parameters

Response

status

mime type

body

Client

Page

page dispatch

parameter passing

Pages and Templates to Java Classes

Navigate to URL

navigate(topic(t){output(t.name)}

<a href=”/topic/FooBar”>FooBar</a>

<a href=”/topic/<%t.id%>”> <%t.name%> </a>

Request URL

GET | POST

Parameters

Response

status

mime type

body

param value

t Foobar

param map

name class

topic

edittopicpage dispatch table

TopicPage

serv

Dispatch

TopicPage.serv

TopicPage.serv

request transaction

TopicPage.serv

handle request

TopicPage.serv

handle request

TopicPage.initVarsAndArgs

TopicPage.loadArguments

TopicPage.loadArguments

Render Page

Render Page

TopicPage.serv

handle post request

TopicPage.serv

handle post request

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

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

Templates

Template Lifecycle

- Store inputs

★ bind request parameters to form inputs

- Validate inputs

★ check validation rules

- Handle action

★ execute selected action

- Render

★ print markup

★ render properties of objects

for each template

render

filter special characters

section nesting

render

rendering WikiText

preventing XSS

render

parameter passing

form

input

binding

submitaction

Forms & Data Binding

issue: bind request parameters to correct binding expressions

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

Repeated Form Elements

multiple instances per page

Form Abstraction

<p> <label for="input221c5e4216d4669e62bee33efc845eb627"> Title </label> <input type="text" value="LoremIpsum" class="inputString" id="input221c5e4216d4669e62bee33efc845eb627" name="input231c5e4216d4669e62bee33efc845eb627"></p>

render

store inputs

<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>

...

render

bind action to action code

handle action

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

render

More Template Issues

- Template calls

★ element parameters

- Nested template definitions

★ closures

- Email templates

★ absolute URLs

- AJAX templates

★ accessible directly from client as page

Access Control

access control implemented by model-to-model transformation

page dispatch takes care of loading & storing session entities

More Compilation by Normalization

- Validation

★ validation rules translated to exceptions and

★ see paper

- Workflow

★ workflow procedures & processes

★ translated to functions, access control, user interface

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