LAB-API-105 — WADL Legacy API Discovery
Purpose
WADL is an XML format for machine-processable descriptions of HTTP-based applications. It was published as a W3C Member Submission, not as a W3C Recommendation. It remains relevant when assessing or modernising legacy services.
Fixture
Task 1 — Build the resource tree
Starting from the resources base URI, draw the complete URI tree. Include:
- path templates;
- matrix, path, query and header parameters;
- methods on each resource;
- request and response representations;
- status codes.
Task 2 — Map methods and representations
Complete:
| Resource | Method | Parameters | Request media type | Success status | Response media type |
|---|
Identify any method that changes state and any method that may return personal data.
Task 3 — Identify description gaps
Record whether the WADL explains:
- authentication and credential location;
- role or scope requirements;
- rate limits;
- idempotency;
- pagination semantics;
- error schemas;
- deprecation and versioning;
- ownership and support contacts.
For each gap, state how you would verify the runtime behaviour safely.
Task 4 — Compare with OpenAPI
Create a mapping from WADL concepts to OpenAPI concepts:
| WADL | OpenAPI equivalent | Migration concern |
|---|---|---|
resources / resource | ||
method | ||
param | ||
representation | ||
response status | ||
grammars |
Checkpoint: Migration is not a syntax-only conversion. Preserve runtime semantics, authentication, error behaviour and backward-compatibility commitments.
Task 5 — Produce a legacy-risk brief
Write a one-page brief that includes:
- current documented surface;
- missing security metadata;
- operational dependencies on WADL tooling;
- proposed OpenAPI migration sequence;
- compatibility and regression tests;
- a rollback plan.
Deliverables
- URI resource tree;
- method/representation matrix;
- description-gap register;
- WADL-to-OpenAPI mapping;
- legacy-risk brief.
Knowledge check
1. What status does WADL have at W3C?
It is a W3C Member Submission from 2009, not a W3C Recommendation.
2. What is the root value of WADL discovery?
The resources element establishes a base URI, under which resource elements define the HTTP application structure.
3. Why must migration include runtime regression testing?
A converted description can appear structurally correct while changing parameter serialization, status codes, authentication expectations, content types or other observable behaviour.