The last few years have seen the development of many SaaS applications, which has led to the development of more and more REST APIs. This large-scale development is happening so fast that today, developers spend almost more time on APIs than on building their applications.
With its OData protocol, Microsoft wanted to solve this problem and make it easier for developers to work with APIs. The two interfaces will therefore unite to communicate and exchange data despite different standards and protocols.
We will try to understand a little better the differences and especially the stakes of all this through this article.
What is OData?
OData is the contraction of the expression Open Data Protocol. It is a technical protocol that should not be confused with Open Data, which is the free access and use of certain data by any user.
To put it simply, OData is an OASIS standard that defines the best practices for creating and consuming RESTful APIs.
As for the latter, REST is the main component of OData. We will come back to this in more detail in the rest of the article. The current version 4.0 dates from 2013.
OData has the particularity to have an ATOM encoding. As a reminder, ATOM is a text editor developed by GitHub for developers based on the XML format. In addition to that, OData will also support JSON format to represent the resources it exposes.
To describe the data exposed in an OData service, a high-level of entity data model (EDM) should be used.
We will consider that an OData resource corresponds to any element of the model that can be exchanged and addressed. Resources are usually represented as entities or collections of entities.
An entity represents a unique instance of an object type and is identified by a primary key. For example, in a customer database, an entity could represent a specific customer with properties such as their name, address, phone number, and so on.
A collection of entities is a set of instances of a particular object type. For example, a collection of customers might include all customer instances in the database.
OData resources can be manipulated by the client using standard HTTP operations such as GET, POST, PUT, and DELETE. For example, a client can retrieve a collection of entities by sending an HTTP GET request to the OData server with the appropriate URL for the collection. The OData server then returns the entities as JSON or XML data in the body of the HTTP response.
What is a REST API?
An API or Application Program Interface is a set of definitions and protocols that we use to develop or integrate software into an application.
In reality, it allows two software programs to communicate through a set of precise rules, whether they have the same language or not. But they are not applications as such.
Indeed, only developers will have access to it and will be able to make it work. An ordinary user will only see the result.
Today, for example, many sites and applications offer to register directly with your Google or Facebook account. This is only possible thanks to an API.
There are several types of APIs: REST, SOAP… Here, we will focus on REST APIs. However, if you want to know more about APIs, don’t hesitate to read our dedicated article.
The term REST (Representational State Transfer) was put forward in the early 2000s by Roy Fielding, known as one of the main authors of the HTTP specification.
A REST service is not an architecture but a set of restrictions that must be taken into account in the software architecture that will be used when creating HTTP web applications.
The Rest APIs allow the development of computer applications by using four basic operations or HTTP requests to access and use data.
We can specify that it will be possible to associate it with a type of SQL request and an HTTP method. Here is a summary of the operations:
- CREATE (SQL: INSERT / HTTP: PUT / POST): allows the creation of resources
- READ (SQL: SELECT / HTTP: GET): retrieve a resource or a collection
- UPDATE (SQL: UPDATE / HTTP: PUT / PATCH): modify or replace a resource
- DELETE (SQL: DELETE / HTTP: DELETE): delete a resource or a collection
In practice, we all use many REST APIs every day, either with the various plugins we install on our browsers or when we use (even unknowingly) external services from an application system or another application.
Today, most APIs are found on SaaS (Software as a service) platforms even if some exist on PaaS (Platform as a service). This implies for companies wishing to offer REST APIs to be able to offer all the features related to the Cloud with a Cloud integration tool that provides connectors and API Rest features.
What are the Differences between API REST and OData?
Differences in Design Principles
API REST and OData have their own principles that differentiate them. We will highlight these.
REST APIs have six principles or constraints that must be respected.
Linking elements together: This principle refers to HATEOS (Hypermedia As The Engine of Application State Hypermedia). It is important to remember that the conformity judgment of an API can be realized thanks to the Richardson model composed of four levels.
- Level 0: RPC: this is the Swamp of POX. This is the simple use of HTTP. There will be only one entry point, that is to say only one URI. Moreover, the only action performed will be a POST action (normally reserved for resource creation). If the API is at this level, it will not be REST but rather SOAP. Indeed, we have seen above that each resource must have its own entry point
- Level 1: resource usage. In this case, each resource will have its endpoint. Note that here, all requests are still made in POST
- Level 2: the use of HTTP verbs, i.e. the CRUD verbs seen previously. The action is no longer part of the URI. It is also at this stage that the status code is set up. As a reminder, these codes indicate whether the HTTP request was successful or not. For example, we can find the code 200 for a successful request or the famous 404 error for a resource that was not found.
- Level 3: This is the HATEOS level which is not often reached by most APIs. It is about putting forward links that users can follow to reach their goals. This way, users will be guided on what to do and will not have to read all the API documentation.
A communication or data transfer is unique and the context must be limited to a simple request. This is due to the number of clients using the API at the same time. If they had to keep something from each request, the memory load would be strongly impacted.
On its side, OData uses all the REST principles and has the advantage of being flexible and of being able to adapt to the use that one has.
Differences in Data Transfer
When a client queries a REST API, it sends an HTTP request to the server using the URI of the desired resource and the appropriate HTTP operation. The server then returns the requested data in the body of the HTTP response. The client can use the information contained in the response to display or manipulate the data.
In OData, data is also transferred using the HTTP protocol and HTTP verbs, but with additional features. OData adds features to facilitate data manipulation, such as pagination, sorting, filtering, and aggregation. These features are available via specific URL parameters.
OData also uses a specific data format, called JSON-LD (JSON Linked Data), which allows for the addition of semantic information to the data. This allows clients to understand the context of the data and use that information to perform more advanced operations.
Differences between Functions
As we said before, the main function of a REST API is to send messages between client and server via HTTP thanks to basic CRUD requests. With OData, it is also possible to send messages via HTTP. Finally, the main difference lies in the exposure of metadata. There are two different ones:
- The document service which uses the ATOM protocol
- An XML document describing the data model (structure, links…)
The language used for this metadata is called Conceptual Schema Definition Language (CSDL).
What to Choose Between API REST and OData?
The choice between API Rest and OData will always depend on your needs and what you want to do with it.
For example, for data retrieval (such as web scraping or data retrieval through URLs), we almost always advise you to choose Rest APIs for their speed and ease of use.
On the other hand, OData seems to be more suitable when communicating between a system and an application.
Moreover, its extensibility is synonymous with the customization and therefore a greater capacity to meet your needs. If your needs are very specific, OData is the right technology for you.
Indeed, RESTful APIs are generally more focused on CRUD operations (create, read, update, delete), while OData provides a more complete set of data access and modification operations.
In addition, OData provides the ability to define custom query options and operations that can be used to add new functionality to a service without changing the underlying service implementation. REST APIs, on the other hand, typically rely on standard HTTP methods to provide functionality.
In summary, while REST APIs provide a simple, lightweight way to expose CRUD operations over HTTP, OData is a more comprehensive protocol for querying and updating data, with a rich set of features for accessing and modifying data, complex types and relationships, custom operations, and more standardized querying.
OData has some advantages over a traditional REST API. First of all, we have seen how easy and intuitive this technology is to use with Java and any other programming language allowing web exchanges. It’s so simple that you can even do it from any URL.
Indeed, when you write an URL, you send information to OData which will answer in XML. Moreover, OData is often preferred because of its extensibility, which allows it to be perfectly adapted to all your needs.
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