How Web Services are introduced in a CLARIN Workflow

1
How Web Services are introduced in a CLARIN
Workflow

• WSDL and WADL files for Web Service description.

2
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

3
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)
• http//www.w3.org/TR/wsdl
• version 2.0
• Used to describe SOAP and REST web services.
  Based on XML.
• (Sun, Canon, IBM, WSO2)
• http//www.w3.org/TR/wsdl20/
• WADL (Web Application Description Language)
• Used to describe REST web services. Based on XML.
• (Sun Microsystems)
• https//wadl.dev.java.net

4
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).

5
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....

6
SOAP Web service example for a CLARIN scenario

• The following web service queries a CQP indexed
  corpus.
• WSDL file url http//igraine.upf.es9100/cqp/serv
  ice.wsdl
• Information included in that WSDL file
• It uses SOAP
• It can be accessed at http//igraine.upf.es9100/c
  qp/api
• It has 3 operations available
• CqpQueryResults GetPendingResults(int ticket_no)
• bool ResultsAvailable(int ticket_no)
• int QueryCqpExpression(string cqp_expression,
  string domain)
• It uses a custom data type CqpQueryResults which
  is also defined in the WSDL file.

7
Using the web service Binding process example
with WSDL. Step 1 Get WS Location

• Look for the Service Tag

ltservice name"CQPService"gt ltport
name"CQPCqpPort" binding"typensCQPCqpBinding"gt
ltsoapaddress location"http//igraine.upf.es9100
/cqp/api"/gt lt/portgt lt/servicegt
8
Binding process example with WSDL. Step 2 Get WS
protocol

• Look for the Binding Tag

ltbinding name"CQPCqpBinding" type"typensCQPCqpP
ort"gt ltsoapbinding transport"http//schemas.xmls
oap.org/soap/http" style"rpc"/gt
9
Binding process example with WSDL. Step 3 Get
Operations available

• Operations are Contained in the operation tag.

ltoperation name"GetPendingResults"gt ltsoapoperati
on soapAction"/cqp/api/GetPendingResults"/gt ltinpu
tgt ltsoapbody encodingStyle"http//schemas.xmlsoa
p.org/soap/encoding/" namespace"urnActionWebServ
ice" use"encoded"/gt lt/inputgt ltoutputgt ltsoapbody
encodingStyle"http//schemas.xmlsoap.org/soap/enc
oding/" namespace"urnActionWebService"
use"encoded"/gt lt/outputgt lt/operationgt
10
Binding process example. Step 4 Get operation
parameters

• Each operation tag is related to the parameters
  description (message tag).

ltoperation name"GetPendingResults"gt . ltmessage
name"GetPendingResults"gt ltpart name"ticket_no"
type"xsdint"/gt lt/messagegt ltmessage
name"GetPendingResultsResponse"gt ltpart
name"return" type"typensCqpQueryResults"/gt lt/me
ssagegt
11
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.

ltoperation name"GetPendingResults"gt . ltmessage
name"GetPendingResultsResponse"gt ltpart
name"return" type"typensCqpQueryResults"/gt lt/me
ssagegt ltxsdcomplexType name"CqpQueryResults"gt
ltxsdallgt ltxsdelement name"error_msg"
type"xsdstring"/gt ltxsdelement name"result"
type"typensCqpResultLineArray"/gt ltxsdelement
name"error" type"xsdboolean"/gt lt/xsdallgt lt/xsd
complexTypegt
12
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 PIDs

13
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.

14
Conclusions

• WSDL/WADL files describe web services interface.
• Any software can be a web service client if the
  web services 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?