Open Data Protocol

In computing, Open Data Protocol (OData) is an open protocol which allows the creation and consumption of queryable and interoperable RESTful APIs in a simple and standard way. Microsoft initiated OData in 2007.^[1] Versions 1.0, 2.0, and 3.0 are released under the Microsoft Open Specification Promise. Version 4.0 was standardized at OASIS,^[2] with a release in March 2014.^[3] In April 2015 OASIS submitted OData v4 and OData JSON Format v4 to ISO/IEC JTC 1 for approval as an international standard.^[4]

The protocol enables the creation and consumption of REST APIs, which allow Web clients to publish and edit resources, identified using URLs and defined in a data model, using simple HTTP messages. OData shares some similarities with JDBC and with ODBC; like ODBC, OData is not limited to relational databases.

Standardization

After initial development by Microsoft, OData became a standardized protocol of the OASIS OData Technical Committee (TC).

OASIS OData Technical Committee

"The OASIS OData TC works to simplify the querying and sharing of data across disparate applications and multiple stakeholders for re-use in the enterprise, Cloud, and mobile devices. A REST-based protocol, OData builds on HTTP, AtomPub, and JSON using URIs to address and access data feed resources. It enables information to be accessed from a variety of sources including (but not limited to) relational databases, file systems, content management systems, and traditional Web sites. OData provides a way to break down data silos and increase the shared value of data by creating an ecosystem in which data consumers can interoperate with data producers in a way that is far more powerful than currently possible, enabling more applications to make sense of a broader set of data. Every producer and consumer of data that participates in this ecosystem increases its overall value."^[5]

TC participants include CA Technologies, Citrix Systems, IBM, Microsoft, Progress Software, Red Hat, SAP SE and SDL.

Architecture

OData is a protocol for the creation and consumption of RESTful APIs. Thus, as common practices of REST, OData builds on HTTP, AtomPub, and JSON using URIs to address and access data feed resources.

Resource identification

OData uses URIs to identify resources. For every OData service whose service root is abbreviated as http://host/service/, the following fixed resources can be found:

The service document

The service document lists entity sets, functions, and singletons that can be retrieved. Clients can use the service document to navigate the model in a hypermedia-driven fashion.

The service document is available at http://host/service/.

The metadata document

The metadata document describes the types, sets, functions and actions understood by the OData service. Clients can use the metadata document to understand how to query and interact with entities in the service.

The metadata document is available at http://host/service/$metadata.

Dynamic resources

The URIs for the dynamic resources may be computed from the hypermedia information in the service document and metadata document.

Resource operation

OData leverages the HTTP verbs to indicate the operations on the resources.

GET: Get the resource (a collection of entities, a single entity, a structural property, a navigation property, a stream, etc.).
POST: Create a new resource.
PUT: Update an existing resource by replacing it with a complete instance.
PATCH: Update an existing resource by replacing part of its properties with a partial instance.
DELETE: Remove the resource.

Resource representation

OData uses different formats for representing data and the data model. In OData protocol version 4.0, JSON format is the standard for representing data, with the Atom format still being in committee specification stage. For representing the data model, the Common Schema Definition Language (CSDL) which defines an XML representation of the entity data model exposed by OData services is used.

A sample OData JSON data payload

A collection of products:

{
  "@odata.context": "http://services.odata.org/V4/OData/OData.svc/$metadata#Products",
  "value": [
    {
      "ID": 0,
      "Name": "Meat",
      "Description": "Red Meat",
      "ReleaseDate": "1992-01-01T00:00:00Z",
      "DiscontinuedDate": null,
      "Rating": 14,
      "Price": 2.5
    },
    {
      "ID": 1,
      "Name": "Milk",
      "Description": "Low fat milk",
      "ReleaseDate": "1995-10-01T00:00:00Z",
      "DiscontinuedDate": null,
      "Rating": 3,
      "Price": 3.5
    },
    ...
  ]
}

A sample OData Atom data payload

A collection of products:

<feed xml:base="http://services.odata.org/V4/OData/OData.svc/" m:context="http://services.odata.org/V4/OData/OData.svc/$metadata#Products" xmlns="http://www.w3.org/2005/Atom" xmlns:d="http://docs.oasis-open.org/odata/ns/data" xmlns:m="http://docs.oasis-open.org/odata/ns/metadata" xmlns:georss="http://www.georss.org/georss" xmlns:gml="http://www.opengis.net/gml">
  <id>http://services.odata.org/v4/odata/odata.svc/Products</id>
  <title type="text">Products</title>
  <updated>2015-05-19T03:38:50Z</updated>
  <link rel="self" title="Products" href="Products"/>
  <entry>
    <id>http://services.odata.org/V4/OData/OData.svc/Products(0)</id>
    <category term="#ODataDemo.Product" scheme="http://docs.oasis-open.org/odata/ns/scheme"/>
    <link rel="edit" title="Product" href="Products(0)"/>
    <link rel="http://docs.oasis-open.org/odata/ns/relatedlinks/Categories" type="application/xml" title="Categories" href="Products(0)/Categories/$ref"/>
    <link rel="http://docs.oasis-open.org/odata/ns/related/Categories" type="application/atom+xml;type=feed" title="Categories" href="Products(0)/Categories"/>
    <link rel="http://docs.oasis-open.org/odata/ns/relatedlinks/Supplier" type="application/xml" title="Supplier" href="Products(0)/Supplier/$ref"/>
    <link rel="http://docs.oasis-open.org/odata/ns/related/Supplier" type="application/atom+xml;type=entry" title="Supplier" href="Products(0)/Supplier"/>
    <link rel="http://docs.oasis-open.org/odata/ns/relatedlinks/ProductDetail" type="application/xml" title="ProductDetail" href="Products(0)/ProductDetail/$ref"/>
    <link rel="http://docs.oasis-open.org/odata/ns/related/ProductDetail" type="application/atom+xml;type=entry" title="ProductDetail" href="Products(0)/ProductDetail"/>
    <title/>
    <updated>2015-05-19T03:38:50Z</updated>
    <author>
      <name/>
    </author>
    <content type="application/xml">
      <m:properties>
        <d:ID m:type="Int32">0</d:ID>
        <d:Name>Bread</d:Name>
        <d:Description>Whole grain bread</d:Description>
        <d:ReleaseDate m:type="DateTimeOffset">1992-01-01T00:00:00Z</d:ReleaseDate>
        <d:DiscontinuedDate m:null="true"/>
        <d:Rating m:type="Int16">4</d:Rating>
        <d:Price m:type="Double">2.5</d:Price>
      </m:properties>
    </content>
  </entry>
  <entry>
    <id>http://services.odata.org/V4/OData/OData.svc/Products(1)</id>
    <category term="#ODataDemo.Product" scheme="http://docs.oasis-open.org/odata/ns/scheme"/>
    <link rel="edit" title="Product" href="Products(1)"/>
    <link rel="http://docs.oasis-open.org/odata/ns/relatedlinks/Categories" type="application/xml" title="Categories" href="Products(1)/Categories/$ref"/>
    <link rel="http://docs.oasis-open.org/odata/ns/related/Categories" type="application/atom+xml;type=feed" title="Categories" href="Products(1)/Categories"/>
    <link rel="http://docs.oasis-open.org/odata/ns/relatedlinks/Supplier" type="application/xml" title="Supplier" href="Products(1)/Supplier/$ref"/>
    <link rel="http://docs.oasis-open.org/odata/ns/related/Supplier" type="application/atom+xml;type=entry" title="Supplier" href="Products(1)/Supplier"/>
    <link rel="http://docs.oasis-open.org/odata/ns/relatedlinks/ProductDetail" type="application/xml" title="ProductDetail" href="Products(1)/ProductDetail/$ref"/>
    <link rel="http://docs.oasis-open.org/odata/ns/related/ProductDetail" type="application/atom+xml;type=entry" title="ProductDetail" href="Products(1)/ProductDetail"/>
    <title/>
    <updated>2015-05-19T03:38:50Z</updated>
    <author>
      <name/>
    </author>
    <content type="application/xml">
      <m:properties>
        <d:ID m:type="Int32">1</d:ID>
        <d:Name>Milk</d:Name>
        <d:Description>Low fat milk</d:Description>
        <d:ReleaseDate m:type="DateTimeOffset">1995-10-01T00:00:00Z</d:ReleaseDate>
        <d:DiscontinuedDate m:null="true"/>
        <d:Rating m:type="Int16">3</d:Rating>
        <d:Price m:type="Double">3.5</d:Price>
      </m:properties>
    </content>
  </entry>
  ...
</feed>

A sample OData metadata document

<edmx:Edmx Version="4.0" xmlns:edmx="http://docs.oasis-open.org/odata/ns/edmx">
  <edmx:DataServices>
    <Schema Namespace="ODataDemo" xmlns="http://docs.oasis-open.org/odata/ns/edm">
      <EntityType Name="Product">
        <Key>
          <PropertyRef Name="ID"/>
        </Key>
        <Property Name="ID" Type="Edm.Int32" Nullable="false"/>
        <Property Name="Name" Type="Edm.String"/>
        <Property Name="Description" Type="Edm.String"/>
        <Property Name="ReleaseDate" Type="Edm.DateTimeOffset" Nullable="false"/>
        <Property Name="DiscontinuedDate" Type="Edm.DateTimeOffset"/>
        <Property Name="Rating" Type="Edm.Int16" Nullable="false"/>
        <Property Name="Price" Type="Edm.Double" Nullable="false"/>
      </EntityType>

      <ComplexType Name="Address">
        <Property Name="Street" Type="Edm.String"/>
        <Property Name="City" Type="Edm.String"/>
        <Property Name="State" Type="Edm.String"/>
        <Property Name="ZipCode" Type="Edm.String"/>
        <Property Name="Country" Type="Edm.String"/>
      </ComplexType>
      
      <EntityContainer Name="DemoService">
        <EntitySet Name="Products" EntityType="ODataDemo.Product"></EntitySet>
      </EntityContainer>
    </Schema>
  </edmx:DataServices>
</edmx:Edmx>

Ecosystem

The ecosystem of OData consists of the client/server libraries that implements the protocol, and applications that is based on the protocol.

Libraries

There are a number of OData libraries available to access/produce OData APIs:

.NET

Server and client: Microsoft's OData .NET libraries
Client: Simple.OData.Client

Java

Server and client: Apache Olingo
Server side: Jello-Framework

JavaScript

Client: Apache Olingo
Client: data.js
Client: JayData for higher level of abstraction (LINQ-like syntax, support for OData geo features, IndexedDB, WebSQL, integration for Kendo UI, Angular.js, Knockout.js and Sencha).
Client: OpenUI5 library maintained by SAP
Client (Node.js): JayData for node
Client: Breeze

Others

Other languages implemented include:^[6]

PHP: odataphp provides OData support for PHP clients.
AJAX: the ASP.NET Ajax Library for getting to OData.
C++: odatacpp_client is a client side only implementation of the OData protocol.
Windward provides OData connection via Microsoft Office templates in either Java or .NET
Reporting tool List & Label has a specialized data provider for OData.
Blackberry (C++): OData-BB10 Open Data Protocol (OData) library for BlackBerry 10 (BB10) Cascades apps
Ruby: ruby_odata library

Applications

Applications include:^[7]

Microsoft Azure exposes an OData API.
SAP NetWeaver Gateway^[8] provides OData access to SAP Business Suite and SAP Business Warehouse.
IBM WebSphere eXtreme Scale REST data service can be accessed by any HTTP client using oData.^[9]
Microsoft SharePoint 2010 and up can expose its data as OData endpoint
Office 365 exposes OData V4.0 APIs.^[10]
Salesforce Lightning Connect consumes OData APIs.^[11]
Tableau can connect to OData APIs.^[12]
elastic.io Integration Platform has an OData connector for integrating with its APIs
TIBCO Spotfire can connect to OData APIs.^[13]
Mulesoft helps integrate with OData APIs.^[14]
SuccessFactors uses Odata APIs

References

^ "Welcome!". MSDN Blogs. OData Team.
^ "OASIS Open Data Protocol (OData) Technical Committee". Retrieved 2013-08-05.
^ "OASIS Approves OData 4.0 Standards for an Open, Programmable Web". oasis-open.org.
^ "OASIS has Submitted OData v4 and OData JSON Format v4 to ISO/IEC JTC 1 for approval as an International Standard". MS Open Tech.
^ "OData OASIS TC Overview".
^ "Libraries". odata.org.
^ "Ecosystem". odata.org.
^ "SAP NetWeaver Gateway". Retrieved 2012-11-22.
^ IBM developerWorks eXtreme Scale REST data service (OData)
^ "Office 365 Unified API Overview".
^ "Salesforce Lightning Connect & OData".
^ "OData".
^ "OData and Spotfire". The TIBCO Blog. Retrieved 2016-03-30.
^ "OData Integration Connector".

External links

OData OASIS Standards

Committee Specifications

Committee Notes

What’s New in OData Version 4.0

[1] "Welcome!". MSDN Blogs. OData Team.

[2] "OASIS Open Data Protocol (OData) Technical Committee". Retrieved 2013-08-05.

[3] "OASIS Approves OData 4.0 Standards for an Open, Programmable Web". oasis-open.org.

[4] "OASIS has Submitted OData v4 and OData JSON Format v4 to ISO/IEC JTC 1 for approval as an International Standard". MS Open Tech.

[5] "OData OASIS TC Overview".

[6] "Libraries". odata.org.

[7] "Ecosystem". odata.org.

[8] "SAP NetWeaver Gateway". Retrieved 2012-11-22.

[IBM_developerWorks_eXtreme_Scale_REST_data_service-9] IBM developerWorks eXtreme Scale REST data service (OData)

[10] "Office 365 Unified API Overview".

[11] "Salesforce Lightning Connect & OData".

[12] "OData".

[13] "OData and Spotfire". The TIBCO Blog. Retrieved 2016-03-30.

[14] "OData Integration Connector".

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