Protocollo Open Data

In informatica, Il Protocollo Open Data (in inglese: Open Data Protocol) o OData è un protocollo aperto che permette la creazione e il consumo di API RESTful interoperabili e interrogabili in maniera semplice e standard. Microsoft creò gli OData nel 2007. Le versioni 1.0, 2.0 e 3.0 sono state rilasciate sotto la licenza Microsoft Open Specification Promise. La versione 4.0 fu standardizzata presso l'OASIS nel marzo 2014. Nell'aprile 2015 OASIS propone gli Odata versione 4 e il formato OData JSON versione 4 all'ISO/IEC JTC 1 per un'approvazione come standard internazionale. Il 23 febbraio 2017 ISO/IEC JTC 1 approva lo standard OData (ISO/IEC 20802-1:2016 ^[1] e ISO/IEC 20802-2:2016 ^[2]) per lo scambio degli Open Data ^[3].

Rappresentazione delle risorse

Esempio di payload OData JSON

A collection of products:

{
  "@odata.context": "http://services.odata.org/V4/OData/OData.svc/$metadata#Products",
  "value": [
    {
      "ID": 0,
      "Name": "Bread",
      "Description": "Whole grain bread",
      "ReleaseDate": "1992-01-01T00:00:00Z",
      "DiscontinuedDate": null,
      "Rating": 4,
      "Price": 2.5
    },
    {
      "ID": 1,
      "Name": "Milk",
      "Description": "Low fat milk",
      "ReleaseDate": "1995-10-01T00:00:00Z",
      "DiscontinuedDate": null,
      "Rating": 3,
      "Price": 3.5
    },
    ...
  ]
}

Un esempio di payload OData Atom

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>

Un esempio di documento metadato OData

<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>

Note

^ ISO/IEC 20802-1:2016 - Open data protocol (OData) v4.0 - Part 1: Core, su iso.org. URL consultato il 23 luglio 2017.
^ ISO/IEC 20802-2:2016 - Open data protocol (OData) v4.0 -- Part 2: OData JSON Format, su iso.org. URL consultato il 23 luglio 2017.
^ OISO/IEC JTC 1 Approves OASIS OData Standard for Open Data Exchange, su oasis-open.org. URL consultato il 23 luglio 2017.

Voci correlate

Collegamenti esterni

(EN) OData.org.
(EN) Open Data Protocol by Example, su msdn.microsoft.com.
(EN) OData Basics Presentation, su hanselman.com.

Standard OData OASIS

OData Version 4.0 Part 1: Protocol, su docs.oasis-open.org.
OData Version 4.0 Part 2: URL Conventions, su docs.oasis-open.org.
OData Version 4.0 Part 3: Common Schema Definition Language (CSDL), su docs.oasis-open.org.
ABNF components - OData ABNF Construction Rules Version 4.0 and OData ABNF Test Cases, su docs.oasis-open.org.
Vocabulary components - OData Core Vocabulary and OData Measures Vocabulary, su docs.oasis-open.org.
XML Schemas - OData EDMX XML Schema and OData EDM XML Schema, su docs.oasis-open.org.
OData JSON Format Version 4.0, su docs.oasis-open.org.

[1] ISO/IEC 20802-1:2016 - Open data protocol (OData) v4.0 - Part 1: Core, su iso.org. URL consultato il 23 luglio 2017.

[2] ISO/IEC 20802-2:2016 - Open data protocol (OData) v4.0 -- Part 2: OData JSON Format, su iso.org. URL consultato il 23 luglio 2017.

[3] OISO/IEC JTC 1 Approves OASIS OData Standard for Open Data Exchange, su oasis-open.org. URL consultato il 23 luglio 2017.

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