How Web Services are introduced in a CLARIN Workflow WSDL and WADL files for Web Service description.

What is needed basically?  In order to include a web service in a general workflow the following data is needed: Protocol used for communication Location of web service List of operations offered by this web service Description of the data types used in those operations

Web Service data files  WSDL (Web service description Language) is a W3C standard version 1.1  Used to describe SOAP web services. Based on XML.  (Microsoft and IBM)  version 2.0  Used to describe SOAP and REST web services. Based on XML.  (Sun, Canon, IBM, WSO2)   WADL (Web Application Description Language)  Used to describe REST web services. Based on XML.  (Sun Microsystems) 

SOAP cannot use WADL  REST Web Services can pack all description data in a WADL file or in a WSDL 2.0 file.  WADL and WSDL languages are essentially the same but WADL is more specific to REST. It is also easier to use.  WADL is not standard (neither is REST) but since WADL is easier to use (like REST) probably will be widely accepted (like REST).

Summing up  WSDL or WADL Description files permit to describe web services  This description is used by client applications to connect to the web services.  For most generic workflows such description files are enough, but for CLARIN....

SOAP Web service example for a CLARIN scenario  The following web service queries a CQP indexed corpus.  WSDL file url:  Information included in that WSDL file: It uses SOAP It can be accessed at It has 3 operations available  CqpQueryResults GetPendingResults(int ticket_no) CqpQueryResults GetPendingResults(int ticket_no)  bool ResultsAvailable(int ticket_no) bool ResultsAvailable(int ticket_no)  int QueryCqpExpression(string cqp_expression, string domain) int QueryCqpExpression(string cqp_expression, string domain) It uses a custom data type CqpQueryResults which is also defined in the WSDL file.

Using the web service: Binding process example with WSDL. Step 1: Get WS Location  Look for the ‘Service’ Tag

Binding process example with WSDL. Step 2: Get WS protocol  Look for the ‘Binding’ Tag …

Binding process example with WSDL. Step 3: Get Operations available  Operations are Contained in the ‘operation’ tag.

Binding process example. Step 4: Get operation parameters  Each ‘operation’ tag is related to the parameters description (‘message’ tag). ….

Binding process example with WSDL. Step 5: Get custom types definition  Operation parameters may have custom data types. Those are described in the ‘ComplexType’ tag and can be nested. …. …

CLARIN Workflows  For general workflows, WSDL or WADL files contain enough information for including the Web Service and use it in any workflow.  Workflows in CLARIN can have more requirements than general workflows that cannot be inside WSDL or WADL files, for instance... Alternative web services / mirrors. Required when errors occur. Information about cost of execution.  WSDL/WADL files use traditional URIs for referencing resources, while CLARIN will use PID’s

Extra information for CLARIN Workflows  Some of this extra information could be contained in the Registry Alternative / mirror web services. Cost of execution  Registry should also have a reversal PID resolution. Get PID using URI. Getting PID using URIs declared in WSDL/WADL files would be easy.

Conclusions  WSDL/WADL files describe web services interface.  Any software can be a web service client if the web service’s WSDL/WADL is available. And it is sufficient to be included in a workflow without human interaction.  CLARIN workflows will have some extra information requirements. With this extra information, user will be able to include web services to CLARIN workflows.  Should the required extra information be in the CLARIN registry?