Mar 21, · How to write a discussion section. Published on March 21, by Shona McCombes. Revised on October 13, The discussion chapter is where you delve into the meaning, importance and relevance of your blogger.com should focus on explaining and evaluating what you found, showing how it relates to your literature review and research questions, and making an argument in support of your ProQuest powers research in academic, corporate, government, public and school libraries around the world with unique content. Explore millions of resources from scholarly journals, books, newspapers, videos and more CHAPTER 5 Representational State Transfer (REST) This chapter introduces and elaborates the Representational State Transfer (REST) architectural style for distributed hypermedia systems, describing the software engineering principles guiding REST and the interaction constraints chosen to retain those principles, while contrasting them to the constraints of other architectural styles
Fielding Dissertation: CHAPTER 5: Representational State Transfer (REST)
This chapter introduces and elaborates the Representational State Dissertation overview REST architectural style for distributed hypermedia systems, describing the software engineering principles guiding REST and the interaction constraints chosen to retain those principles, while contrasting them to the constraints of other architectural styles.
REST is a hybrid style derived from several of the network-based architectural styles described in Chapter 3 and combined with additional constraints that define a uniform connector interface. The software architecture framework of Chapter 1 is used to define the architectural elements of REST and examine sample process, dissertation overview, connector, and data views of prototypical architectures.
The design rationale behind the Web dissertation overview can be described by an architectural style consisting dissertation overview the set of constraints applied to elements within the architecture.
By examining the impact of each constraint as dissertation overview is added to the evolving style, we can identify the properties induced by the Web's constraints. Additional constraints can then be applied to form a new architectural style that better reflects the desired properties of a modern Web architecture.
This section dissertation overview a general overview of REST by walking through the process of deriving it as an architectural style. Later sections will describe in more detail the specific constraints that compose the REST style. There are two common perspectives on the process of dissertation overview design, whether it be for buildings or for software.
The first is that dissertation overview designer starts with nothing--a blank slate, whiteboard, or drawing board--and builds-up an architecture from familiar components until it dissertation overview the needs of the intended system, dissertation overview.
The second is that a designer starts with the system needs as a whole, without constraints, and then incrementally identifies and applies constraints to elements of the system in order to differentiate the design space and allow the forces that influence system behavior to flow naturally, in harmony with the system. Where the first emphasizes creativity and unbounded vision, the second emphasizes restraint and understanding of the system context.
REST has been developed using the latter process. Figures through depict this graphically in terms of how the applied constraints would differentiate the process view of an architecture as the incremental set of constraints is applied. The Null style Figure is simply an empty set of constraints. From an architectural perspective, the null style describes a system in which there are no distinguished boundaries between components. It is the starting point for our description of REST.
The first constraints added to our hybrid style are those of the client-server architectural style Figuredescribed in Section 3. Separation dissertation overview concerns is the principle behind the client-server constraints.
By separating the user interface concerns from the data storage concerns, we improve the portability of the user interface across multiple platforms and improve scalability by simplifying the server components. Perhaps most significant to the Web, dissertation overview, however, is that the separation allows the components to evolve independently, thus supporting the Internet-scale requirement of multiple organizational domains. We next add a constraint to the client-server interaction: communication must be stateless in nature, dissertation overview, as in the client-stateless-server CSS style of Section 3.
Session state is therefore kept entirely on the client, dissertation overview. This constraint induces the properties of visibility, reliability, dissertation overview, and scalability.
Visibility is improved because a monitoring system does not have to look beyond a single request datum in order to determine the dissertation overview nature of the request. Reliability is improved because it eases the task of recovering from partial failures [ ]. Scalability is improved because not having to store state between requests allows the server component to quickly free resources, and further simplifies implementation because the server doesn't have to manage resource usage across requests.
Like most architectural choices, the stateless constraint reflects a design trade-off. The disadvantage is that it may decrease network performance by increasing dissertation overview repetitive data per-interaction overhead sent in a series of requests, since that data cannot be left on the server in a shared context.
In addition, placing the application state on the client-side reduces the server's control over consistent application behavior, since the application becomes dependent on the correct implementation of semantics dissertation overview multiple client versions. In order to improve network efficiency, dissertation overview, we add cache constraints to form the client-cache-stateless-server style of Section 3.
Cache constraints require that the data within a response to a request be implicitly or explicitly labeled as cacheable or non-cacheable.
If a dissertation overview is cacheable, dissertation overview, then a client cache is given the right to reuse that response data for later, equivalent requests.
The advantage of adding cache constraints is that they have the potential to partially or completely eliminate some interactions, improving efficiency, scalability, and user-perceived performance by reducing the average latency of a series of interactions.
The trade-off, however, dissertation overview, is that a cache can decrease reliability if stale data within the cache differs significantly from the data that would have been obtained had the request been sent directly to the server. The early Web architecture, as portrayed by the diagram in Figure [ 11 ], was defined by the client-cache-stateless-server set of constraints.
That is, dissertation overview design rationale presented for the Web architecture prior to focused on stateless client-server interaction for the exchange of static documents over the Internet, dissertation overview.
The protocols for communicating interactions had rudimentary support for non-shared caches, but did not constrain the interface to a consistent set of semantics for all resources. Instead, the Web relied dissertation overview the use of a common client-server implementation library CERN libwww to maintain consistency across Web applications. Developers of Web implementations had already exceeded the early design. In addition to static documents, requests could identify services that dynamically generated responses, dissertation overview, such as image-maps [Kevin Hughes] and server-side scripts [Rob McCool], dissertation overview.
Work had also begun on intermediary components, in the form dissertation overview proxies [ 79 ] dissertation overview shared caches [ 59 ], but extensions dissertation overview the protocols were needed in order for them to communicate reliably. The following sections describe the constraints added to the Web's architectural style in order to guide the extensions that form the modern Web architecture.
The central feature that distinguishes the REST architectural style from other network-based styles is its emphasis on a uniform interface between components Figure By applying the software engineering principle of generality to the component interface, dissertation overview, the overall system architecture is simplified and the visibility of interactions is improved.
Implementations are decoupled from the services they provide, which encourages independent evolvability. The trade-off, dissertation overview, though, is that a uniform interface degrades efficiency, since information is transferred in a standardized form rather than one which is specific to an application's needs. The REST interface is designed to be efficient for large-grain hypermedia data transfer, optimizing for the common case of the Web, but resulting in an interface that is not optimal for other forms of architectural interaction.
In order to obtain a uniform interface, multiple architectural constraints are needed to guide the behavior of components. REST is defined by four interface constraints: identification of resources; manipulation of resources through representations; self-descriptive messages; and, hypermedia as the engine of application state, dissertation overview.
These constraints will be discussed in Section 5. In order to further improve behavior for Internet-scale requirements, we add layered system constraints Figure As described in Section 3. By restricting knowledge of the system to a single layer, we place a bound on the overall system complexity and promote substrate independence. Layers can be used to encapsulate legacy services and to protect new services from legacy clients, dissertation overview, simplifying components by moving infrequently used functionality to a shared intermediary.
Intermediaries can also be used to improve system scalability by enabling load balancing of services across multiple networks and processors. The primary disadvantage of layered systems is that they add overhead and latency dissertation overview the processing of data, reducing user-perceived performance [ 32 ].
For a network-based system that supports cache constraints, this can be offset by the benefits of shared caching at intermediaries. Placing shared caches at the boundaries of an organizational domain can result in significant performance benefits [ ]. Such layers also allow security policies to be enforced on data crossing the organizational boundary, as is required by firewalls [ 79 ]. The combination of layered system and uniform interface constraints induces architectural properties similar to those of the uniform pipe-and-filter style Section 3.
Although REST interaction is two-way, the large-grain data flows of hypermedia interaction can each be processed like a data-flow network, with filter dissertation overview selectively applied to the data stream in order to transform the content as it passes [ 26 ], dissertation overview. Within REST, intermediary components can actively transform the content of messages because the messages are self-descriptive and their semantics are visible to intermediaries.
The dissertation overview addition to our constraint set for REST comes from the code-on-demand style of Section 3. REST allows client functionality to be extended by downloading and executing code in the form of applets or scripts. This simplifies clients by reducing the dissertation overview of features required to be pre-implemented.
Allowing features to be downloaded after deployment improves system extensibility. However, it also reduces visibility, and thus is only an optional constraint within REST. The notion of an optional constraint may seem like an oxymoron. However, dissertation overview, it does have a purpose in the architectural design of a system that encompasses multiple organizational boundaries. It means that the architecture only gains the benefit and suffers dissertation overview disadvantages of the optional constraints when they are known to be in effect for some realm of the overall system.
For example, if all of the client software within an organization is known to support Java applets [ 45 ], dissertation overview, then services within that organization can be constructed such that they gain the benefit of enhanced functionality via downloadable Java classes.
At the same time, however, the organization's firewall may prevent the transfer of Java applets from external sources, and thus to the rest of the Web it will appear as if those clients do not support code-on-demand. An optional constraint allows us to design an architecture that dissertation overview the desired behavior in the general case, but with the understanding that it may be disabled within some contexts. REST consists of a set dissertation overview architectural constraints chosen for the properties they induce on candidate architectures.
Although each of these constraints can be considered in isolation, describing them in terms of their derivation from common architectural styles makes it easier to understand the rationale behind their selection.
Figure depicts the derivation of REST's constraints graphically in terms of the network-based architectural styles examined in Chapter 3. 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, dissertation overview.
It encompasses the fundamental constraints upon components, connectors, and data that define the basis of the Web architecture, and dissertation overview the essence of its behavior as a network-based application.
Unlike the distributed object style [ 31 ], where all data is encapsulated within and hidden by the processing components, the nature and state of an architecture's data elements is a key aspect of REST. The rationale for this design can dissertation overview seen in the nature dissertation overview distributed hypermedia. When a link is selected, information needs to be moved from the location where it is stored to the location where it will be used by, dissertation overview, in most cases, a human reader.
This is unlike many other distributed processing paradigms [ 650 ], dissertation overview, where it is possible, and usually more efficient, to move the "processing agent" e. to the data rather than move the data to the processor. A distributed hypermedia architect has only three fundamental options: 1 render the data where it is located and send a fixed-format image to the recipient; 2 encapsulate the data with a rendering engine and send both to the recipient; or, 3 send the raw data to the recipient along with metadata that describes the data type, so that the recipient can choose their own rendering engine.
Each option has its advantages and disadvantages. Option 1, the traditional client-server style [ 31 ], allows all information about the true dissertation overview of the data to remain hidden within the sender, preventing assumptions from being made about the data structure and making client implementation easier, dissertation overview. However, it also severely restricts the functionality of the recipient and places most of the processing load on the sender, leading to scalability problems.
Option 2, dissertation overview, the mobile object style [ 50 ], provides information hiding while enabling specialized processing of the data via its unique rendering engine, but limits the functionality of the dissertation overview to what is anticipated within that engine and may vastly increase the amount of data transferred. Option 3 allows the sender to remain simple and scalable while minimizing the bytes transferred, but loses the advantages of information hiding and requires that both sender and recipient understand the same data types, dissertation overview.
REST provides a hybrid of all three options by focusing on a dissertation overview understanding of data types with metadata, but limiting the scope of what is revealed to a standardized interface. REST components communicate by transferring a representation of a resource in a format matching one of an evolving set of standard data types, selected dynamically based on the capabilities or desires of the recipient and the nature of the resource.
Whether the representation is in the same format as the raw source, or is derived from the source, dissertation overview, remains hidden behind the interface, dissertation overview. The benefits of the mobile object style are approximated by sending a representation that consists of instructions in the standard data format of an encapsulated rendering engine e.
REST therefore gains the separation of concerns of the client-server style without dissertation overview server scalability problem, allows information hiding through a generic interface to enable encapsulation and evolution of services, and provides for a diverse set of functionality through downloadable feature-engines. The key abstraction of information in REST is a resource. Any information that can be named can be a resource: a document or image, a temporal service e.
a personand so on.
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About TCC TCC provides flexible, affordable education options to over 30, students each year, both online and on campuses and centers in all major cities in South Hampton Roads. Learn More Mar 21, · How to write a discussion section. Published on March 21, by Shona McCombes. Revised on October 13, The discussion chapter is where you delve into the meaning, importance and relevance of your blogger.com should focus on explaining and evaluating what you found, showing how it relates to your literature review and research questions, and making an argument in support of your ProQuest powers research in academic, corporate, government, public and school libraries around the world with unique content. Explore millions of resources from scholarly journals, books, newspapers, videos and more
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