OData Standard: The Protocol for REST API

Open Data Protocol, commonly known as OData, is used for creating interoperable and queryable REST APIs in a more convenient way. REST APIs are generally used by web clients for publishing or editing resources. Data services based on REST APIs allow resource identification using URLs and define them in Entry Data Models. Web clients can edit or publish those data and information using HTTP messages within the OData ecosystem.

OData standard enables information accessibility from different types of sources including traditional websites, file systems and relational databases. It is used for increasing the data shared value by breaking down data silos. It allows data producers to interoperate with data consumers in a convenient way.

Advantages of OData Standard

  • Developers use this protocol to interact with information through REST services.
  • One can create custom methods.
  • It doesn’t require creating a proxy class like a web service.
  • It provides metadata about a service interface which is used for generating client code for service access.
  • It supports generic queries for data filtering on the client side.

The OASIS Open Standards Consortium has approved OData 4.0 and OData JSON format 4.0 as international standards for open data exchange. Draft of the latest version of OData protocol, known as OData 4.01, has been published by OASIS as a committee specification. While OData 4.0 proves to be a suitable protocol for creating REST APIs, the recent version not only adds a variety of new features but also removes few restrictions from the previous version. These modifications are based on –

  • Simplified syntax
  • Extended query language
  • Simplified payloads

New features related to syntax and query language are supported to OData 4.0 as extensions.

New Features of OData 4.01

Some of the new features of OData 4.01are mentioned below:

1. Default namespace: OData 4.0 used to reference model elements with qualified names that are added as prefixes with model element namespace. The latest version defines a default namespace as a reference to a model element instead of qualified names.

2. Schema versioning: OData 4.01 allows schema versioning, i.e. same URL service root can be used for serving old as well as new schema.

3. Isolation of Header without prefix: The latest version accepts header isolation without using OData prefix.

4. Omit values: OData 4.01 reduces the message size of a sparsely populated entity with multiple properties by omitting null and default values.

5. Ordered collections: Unlike version 4.0 that treats a collection as an unordered list of stuff; OData 4.01 follows ordered collection and allows zero based indexing method for inserting as well as updating items of a collection.

6. Deep update: With this new feature, one can create or update entities with update payload containing nested entities.

7. Alternate keys: Entities can now contain alternate keys along with primary keys for parentheses style key syntax.

8. ‘matchesPattern’ function: OData 4.01 introduces a new function called ‘matchesPattern’ that is used for checking similarities between a string and a regular expression.

OData 4.01 service is compatible with clients of the previous version; ODataVersion header facilitates content negotiation to ensure that version 4.0 clients don’t experience unexpected constructs within response payloads.

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