The Representational State Transfer (REST) style is an abstraction of the architectural elements within a distributed hypermedia system. REST ignores the details of component implementation and protocol syntax in order to focus on the roles of components, the constraints upon their interaction with other components, and their interpretation of significant data elements.
It encompasses the fundamental constraints upon components, connectors, and data that define the basis of the Web architecture, and thus the essence of its behavior as a network-based application. REST distinguishes three classes of architectural elements, they are:
- Connectors
- Components
- Data Elements
Connectors
Connectors represent the activities involved in accessing resources and transferring representations. Roles provide an interface for components to implement. REST encapsulates different activities of accessing and transferring representations into different connector types. The table below summarizes the connector types:
| Connector Type | Description | Example |
| Client | Sending requests, receiving responses. | HTTP library |
| Server | Listening for requests, sending responses. | Web Server API |
| Cache | Can be located at the client or server connector to save cacheable responses, can also be shared between several clients | Browser cache |
| Resolver | Transforms resource identifiers into network addresses. | bind (DNS lookup library) |
| Tunnel | Relays requests, any component can switch from active behavior to a tunnel behavior. | SOCKS, SSL after HTTP CONNECT |
Components
In REST, the various software that interacts with one another are called components. They are categorized by roles summarized in the table below:
| Component Role | Description | Example |
| Origin Server | Uses a server connector to receive the request, and is the definitive source for representations of its resources. Each server provides a generic interface to its services as a resource hierarchy. | Apache httpd, Microsoft IIS |
| User Agent | Uses a client connector to initiate a request and becomes the ultimate recipient of the response. | Browser like Netscape Navigator etc |
| Gateway | Act as both, client and server in order to forward - with possible translation - requests and responses. | Squid, CGI, Reverse Proxy |
| Proxy | CERN Proxy, Netscape Proxy, Gauntlet |
Data Elements
The key aspect of REST is the state of the data elements, its components communicate by transferring representations of the current or desired state of data elements.
REST identifies six data elements: a resource, resource identifier, resource metadata, representation, representation metadata, and control data, shown in the table below:
Addressable means anything that can be accessed and transferred between clients and servers
REST identifies six data elements: a resource, resource identifier, resource metadata, representation, representation metadata, and control data, shown in the table below:
| Data Element | Description | Example |
| Resource | Any information that can be named is a resource. A resource is a conceptual mapping to a set of entities, not the entity itself. | Title of a movie from IMDb, A Flash movie from YouTube, Images from Flickr etc |
| Resource Identifier | Every resource must have a name that uniquely identifies it. Under HTTP these are called URIs. Uniform Resource Identifier (URI) in a RESTful system is a hyperlink to a resource. It is the only means for clients and servers to exchange representations of resources. The relationship between URIs and resources is many to one. A resource can have multiple URIs which provide different information about the location of a resource. | |
| Resource metadata | This describes the resource. A metadata provides additional information such as location information, alternate resource identifiers for different formats or entity tag information about the resource itself. | Source link, vary |
| Representation | It is something that is sent back and forth between clients and servers. So, we never send or receive resources, only their representations. A representation captures the current or intended state of a resource. A particular resource may have multiple representations | Sequence of bytes, HTML document, archive document, image document |
| Representation metadata | This describes the representation. | Headers (media-type) |
| Control data | This defines the purpose of a message between components, such as the action being requested. | If-Modified-Since, If-Match |
Details of the standardized format of a URI are as follows:
scheme://host: port/path?queryString#fragment
- scheme - It is the protocol you are using to communicate with. For RESTful web services, it is usually HTTP or HTTPS
- host - It is a DNS name or IP address
- port - This is optional and which is numeric The host and port represent the location of your resource on the network
- path - This expression is a set of text segments delimited by the “/” character. Think of the path expression is a directory list of a file on your machine
- ? - This character separates the path from the queryString. queryString -This is a list of parameters represented as name/value pairs. Each pair is delimited with the “&” character. Here’s an example query string within a URI: http://somedomain.com/customers?firsttName=Manisha&zipcode=411027
- fragment: It is delimited by a “#” character. The fragment is usually used to point to a certain place in the document you are querying
Conclusion
In this post, we have discussed different REST Architectural Elements -
- Connectors
- Components
- Data Elements
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