Web-based Services

SOAP - Simple Object Access Protocol

• Messages are encoded in Xml
• The format is defined by SOAP
• Envelope
• Headers (not the same as HTTP headers)
• Body - contains the data/payload and an Operation (verb) name that maps to some code method on the Server
• Several protocols collectively referred to as WS-* protocols (e.g. WSDL, MEX)
• Uses HTTP POST

POX - Plain Old Xml

• Transfer of XML data over HTTP
• XML is application defined. Often an XML Schema is provided
• HTTP GET to a URI fetches the desired data
• A client can specify preferred format in the HTTP header to get data in the desired format, such as XML, JSON, or AtomPub (if supported by the Service)
• Accept: application/json, application/atom+xml
• HTTP POST to a URI modifies the desired data

REST - REpresentational State Transfer

• Services are exposed as "resources" (URIs). Example, http://WeatherService.com/USA/CA/SANDIEGO would return the whether for San Diego, California
• CRUD operations on a resource (URI) are defined by HTTP verbs such POST, GET, PUT, and DELETE, respectively
• GET to a given URI may retrieve requested data or entity; POST to the same URI may add a new data or entity

Atom

• A specific dialect of XML
• Extensible, older clients simply ignore extra data
• Leverages REST to communicate

Atom+Pub

• XML format similar to Atom but extended to provide more functionality
• Builds on Atom by supporting retrieval and editing (publishing) of web resources

OData

• Extends Atom+Pub to provide RESTful data services for exchanging data over the Web
• Provides a standard way of editing and querying data
• Conventions for representing entities in AtomPub
• Query string conventions for addressing, filtering and paging data
• Constrained HTTP Operations for submitting requests
• Metadata support to learn about the service
• Based on HTTP, AtomPub, JSON
• Can expose different data sources (db, files,...) uniformly
• Can use LINQ from .NET client to send OData (RESTful) requests