WSDL - Service Registry

1. What is a Service Registry?

A Service Registry is a centralized directory or repository where Service Providers publish their WSDL documents and Service Consumers search for and discover available services.

Think of it like a phonebook for web services:

  • Service Providers → Publish their WSDL.

  • Service Consumers → Search the registry to find the WSDL and understand how to call the service.

2. Role of Service Registry in Web Services Architecture

In a WSDL-based SOA (Service-Oriented Architecture), the Service Registry acts as the middleman between providers and consumers.

Key Responsibilities

  1. Stores WSDL Documents

    • Providers publish service descriptions (WSDL).

  2. Supports Discovery

    • Consumers query the registry to find services.

  3. Maintains Metadata

    • Stores details like:

      • Service name

      • Service operations

      • Endpoint URLs

      • Protocols used

      • Service version

  4. Improves Reusability

    • One WSDL can be reused by multiple consumers.

  5. Facilitates Loose Coupling

    • Consumers don’t need to know where the provider is — they just search for services dynamically.

3. How Service Registry Works

The process involves three main steps: Publish → Discover → Bind.

Step 1 — Publish (By Service Provider)

  • The Service Provider creates a WSDL.

  • Publishes the WSDL document to the Service Registry.

  • Example:

    Service Name: CustomerService
Endpoint: http://example.com/services/customer
WSDL URL: http://example.com/services/customer?wsdl

Step 2 — Discover (By Service Consumer)

  • The Service Consumer queries the registry to find available services.

  • Searches by:

    • Service name

    • Category

    • Business name

    • Keywords

  • The registry returns WSDL URLs for matching services.

Step 3 — Bind (Consumer Uses WSDL)

  • The Service Consumer downloads the WSDL.

  • Generates client code using tools (wsimport, svcutil, etc.).

  • Invokes the service directly using the endpoint defined in the WSDL.

4. UDDI – The Standard Service Registry

Historically, UDDI (Universal Description, Discovery, and Integration) was the standard specification for service registries.

UDDI Components

  1. White Pages → Business details (name, contact info)

  2. Yellow Pages → Categorization of services (industry, type)

  3. Green Pages → Technical details (WSDL URLs, bindings, endpoints)

UDDI Operations

Operation Purpose
publish Provider registers a WSDL
find_service Consumer searches for WSDL
get_serviceDetail Retrieves service metadata
delete_service Removes WSDL from registry

Example UDDI Registries:

  • jUDDI (Apache project)

  • IBM WebSphere Service Registry

  • Oracle Service Registry

5. Example Scenario

Actors:

  • Provider → ABC Bank

  • Consumer → XYZ Corp

  • Registry → UDDI Directory

Step 1: ABC Bank Publishes WSDL

  • ABC Bank registers AccountService WSDL in the UDDI registry:

    Service Name: AccountService
WSDL URL: http://abcbank.com/ws/account?wsdl
Endpoint: http://abcbank.com/ws/account

Step 2: XYZ Corp Searches UDDI

  • XYZ searches for “AccountService” in the registry.

  • The registry returns the WSDL URL and endpoint.

Step 3: XYZ Corp Generates Client Code

  • XYZ uses:

    wsimport http://abcbank.com/ws/account?wsdl

  • Generates proxy classes.

  • Calls:

    AccountService service = new AccountService();
AccountPort port = service.getAccountPort();
double balance = port.getBalance(101);

6. Service Registry Architecture

The architecture involves three main roles:

Role Action
Service Provider Publishes WSDL to registry
Service Registry Stores WSDL, allows discovery
Service Consumer Searches registry, downloads WSDL, and invokes service

Workflow:

  1. Provider → Publishes WSDL to registry.

  2. Consumer → Searches registry.

  3. Registry → Returns WSDL info.

  4. Consumer → Generates client code & binds to provider.

7. Modern Alternatives to UDDI

While UDDI was the official standard, it is rarely used today.
Modern alternatives include:

  • API Gateways (e.g., Kong, Apigee, AWS API Gateway)

  • Service Discovery Tools (e.g., Consul, Eureka, Zookeeper)

  • Swagger / OpenAPI → REST-based WSDL equivalent

  • GraphQL Schema Registries

8. Real-Life Analogy

Think of a Service Registry like Google Play Store:

  • App Developer (Provider) → Uploads app → Publishes metadata.

  • Play Store (Registry) → Stores app info, categorizes it.

  • User (Consumer) → Searches app → Installs it.

Similarly:

  • Provider publishes WSDL → Registry stores it.

  • Consumer searches registry → Finds WSDL → Uses service.