15 May 2007 IVOA Beijing: Grid & Web Services 21 Matthew J. Graham (Caltech, NVO) T HE US N ATIONAL V IRTUAL O BSERVATORY vs

15 May 2007 IVOA Beijing: Grid & Web Services 22 What is REST? Representational State Transfer (Fielding 2000) A resource-oriented architectural style for web services based on the WWW architecture: –Each resource has a unique identifier (URI) –Resource representations are exchanged in XML over HTTP –Agents employ the HTTP methods as a standard API to ensure uniform interface semantics REST is about exposing resources through URIs and not services through messaging interfaces REST is possible with SOAP and WSDL 2.0

15 May 2007 IVOA Beijing: Grid & Web Services 23 RESTful interfaces HTTP method DescriptionHTTP status codes GETView resource representation200, 301, 400 PUTCreate/Modify client-identified resource 200, 301, 400, 410 POSTCreate/Modify server-identified resource 201, 400 DELETEDelete resource200, 204 GET is safe: it has no side effects and is purely for retrieval GET, PUT, and DELETE are idempotent: the side-effect of N > 0 identical requests is the same as for a single request Atom Publishing Protocol is the canonical REST interface WebDAV is not RESTful: URLs are inherently hierarchical and not opaque properties and locks are not separate resources PROPPATCH, PROPFIND, LOCK and UNLOCK methods manipulate metadata attached to a resource 207 (Multi-Status) response code for bundled operations

15 May 2007 IVOA Beijing: Grid & Web Services 24 WS-* (18 months ago) WS-I Basic Profile WS-I Basic Security Profile WS-Manageability WS-Management WS-MetadataExchange WS-Notification WS-Policy WS-PolicyAssertions WS-PolicyAttachment WS-PolicyFramework WS-Polling WS-Provisioning WS-Reliability WS-ReliableMessaging WS-RemotePortals WS-ResourceFramework WS-ResourceLifetime WS-ResourceProperties WS-Routing WS-SecureConversation WS-Security WS-SecurityPolicy WS-Addressing WS-AtomicTransaction WS-Attachments WS-BaseNotification WS-BPEL WS-BrokeredNotification WS-BusinessActivity WS-CAF WS-Choreography WS-CDL WS-Context WS-Coordination WS- CoordinationFramework WS-Discovery WS- DistributedManagement WS-Enumeration WS-Eventing WS-ExperienceLanguage WS-Federation WS-GAF WS-Inspection WSIL WS-Semantics WS-Topic WS-Transaction WS-Transaction Management WS-Transfer WS-Trust ASAP ebXML MTOM SAML SOAP SwA UBL UDDI WSDL XACML XML Encryption XML Signature XKMS + others incl. WS- KitchenSink

15 May 2007 IVOA Beijing: Grid & Web Services 25 Description languages - I WSDL: –Complicated –Difficult to describe protocols that use SOAP headers so not straightforward for WS-* –Operation-centric –Web service versioning is difficult (better in WSDL 2.0) –Limited modelling of interaction patterns (no more than two messages within a single exchange) –No choreographic information so cannot specify ordering constraints between operations –WSDL is immutable so no dynamic endpoints

15 May 2007 IVOA Beijing: Grid & Web Services 26 Description languages - II WSDL 1.1: –Supports HTTP GET and POST –Cannot use GET with no parameters –Cannot mix multiple HTTP methods on one port WSDL 2.0: –Supports HTTP GET/PUT/POST/DELETE –No support for JSON or binary format (need to write specification for binding rules on how to serialize) –Authentication limited to HTTP Basic and Digest –No support for links: cannot write WSDL for Atom Publishing Protocol WADL: –Backed by Sun (wadl.java.dev.net - wadl2java) – –REST Describe (

15 May 2007 IVOA Beijing: Grid & Web Services 27 Sample WADL file <application xmlns=" xmlns:xsi=" xmlns:xsd=" xmlns:vot=" xsi:schemaLocation=" wadl.xsd">

15 May 2007 IVOA Beijing: Grid & Web Services 28 Security WS-Security: –provides message level, end-to-end security –really requires WS-SecurityPolicy –interoperable implementations? HTTP Basic: –Base64-encoded username/password HTTP Digest: –MD5 hashes of username, password, authentication realm, etc. SSL/TLS: –provides transport level, point-to-point security Message authentication: –AWS approach using HMAC with SHA-1 hash code HTTPSec for full message level security

15 May 2007 IVOA Beijing: Grid & Web Services 29 Addressing + state WS-Addressing: –SOAP lacks a standard way to specify where a message is going, how to return a response or where to report an error –provides SOAP header keywords such as: To, ReplyTo, FaultsTo, Anonymous, and MessageId/RelatesTo. –SAF (Store-and-forward) service is a use case that REST cannot address WSRF: –framework for handling state –separates web service and state information (resource) –a resource has a unique key and message exchanges with the service are used to interact with the resource –basically equivalent to REST