OData – stands for Open Data Protocol – and is a protocol that SAP is using to make SAP data accessible to the world so that even developers who don’t understand SAP lingo can be able to use this data and develop Web Applications, Websites and Mobile Apps
What is OData (Open Data Protocol)?
OData (Open Data Protocol) is an open protocol for sharing data.
In other words, any client can access the data from any data source.
It is a service layer on top of the OData Model and it exposes an endpoint that allows the client to access the data using OData Protocol and OData Client library.
It converts the different format of data into a common format for the client to use.
OData protocol lets a client make requests to and get responses from an OData service.
OData protocol is a set of RESTful interactions.
OData protocol is just like HTTP and used to do CRUD operation by using OData. It transfers the data in form of XML or JSON.
OData Model is used to represent the data from the different data source in a single format using Entity Data model (EDM).
Representational State Transfer is a style of software architecture for distributed systems such as the World Wide Web.
REST uses the standard GET, PUT, POST & DELETE methods and other existing features of the HTTP protocol.
HTTP methods in OData:
OData also offer more than just exposing content, it offers full CRUD support by using the different HTTP methods:
GET: Gets one or many entries.
POST: Create a new entry.
PUT: Update an existing entry
DELETE: Remove an entry.
This series of blogs is an attempt to provide a comprehensive guide to OData and how it is consumed in the SAP world. There has been a lot of content on the Internet explaining what is OData, how the services and published and how to consume which is scattered and assumes that the reader has clarity already on some very important fundamentals. However, there are so many aspects which deserve more than just a mention. In this blog, we will try and cover the topic 360 degrees.
We start with the very basics of HTTP and then gradually build on to OData and finally conclude with a detailed end-to-end exercise on how to create an OData service and how to consume it.
How Internet Works?
It might sound to be an unrelated topic when the focus is on OData. HTTP is the common thread between the two. HTTP is the underlying protocol on which OData is based and also one of the most common languages which are spoken on the Internet.
You would typically need a Web Browser, address of the document you want to read or the URL (Uniform Resource Locator), a Web Server running at the system where the document is located.
Web Browser is a software which is responsible for retrieving and presenting resources on the web. Web Browser parses the HTML response received from the Web and prepares a DOM Tree. DOM stands for Document Object Model and it is a language-independent convention of representing objects in HTML. Web Browser acts as an interface between you and the World Wide Web.
You can request for a document located somewhere on this planet by providing its address via the browser which sends HTTP requests to the webserver. The Web server then sends back HTTP response that is parsed by the Web Browser for you to view the document on your machine.
HTTP stands for HyperText Transfer Protocol and as the name suggests it defines the semantics of what the browser and the web server can communicate to each other. The how part of the communication or the byte by byte transfer of the data packets across the network is not HTTP but it is done via TCP/IP protocols.
An important component in the story so far is also the Web Server. In a nutshell, Web Server is a server program which sits on a physical server and waits for requests from a client. Whenever a request is received the Web Server prepares a response and sends it back to the client using the HTTP protocol. It is important to note that HTTP is not the only but, by far the most commonly used protocol and that the client here can be a browser or any other software that communicates in HTTP.
Let us now try and put up a formal definition to the HTTP.
“HTTP is based on a Client-Server architecture style and it uses a stateless request/response protocol to communicate between the client and the webserver. The HTTP protocol helps define what requests can be sent across by the client and response sent by the webserver. The communication of data over the network is however done using on TCP/IP protocol”.
It is evident that HTTP is based on client-server architecture from our description till now, the browser is the client which sends HTTP request and web server which sends the response back to the browser. But, why stateless?
Every single HTTP request that is received by the webserver is forgotten after a response has been sent across. Web servers do not process an HTTP request by remembering the previous request.
URI and URL are not the same things
We mentioned a while back that you need to know the URL of the document you wish to view in your browser. Can I not mention a URI as an address to get the document on the web? Let us quickly understand the difference between the two.
URI or the Uniform Resource Identifier can be classified as a name, locator or both that identifies a resource uniquely.
URL (Uniform Resource Locator) is a subset of URI that not only identifies a resource uniquely but also provide means of locating the resource.
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