The http server is replaced. Perhaps even the method of generating responses for all of the content is replaced. However, what doesn't need to change is the web interface: if designed correctly, the namespace on the new server can mirror that of the old, meaning that from the client's perspective, which only knows about resources and not about how they are implemented, nothing has. 6.2.4 Binding Semantics to uri as mentioned above, a resource can have many identifiers. In other words, there may exist two or more different uri that have equivalent semantics when used to access a server. It is also possible to have two uri that result in the same mechanism being used upon access to the server, and yet those uri identify two different resources because they don't mean the same thing. Semantics are a by-product needed of the act of assigning resource identifiers and populating those resources with representations. At no time whatsoever do the server or client software need to know or understand the meaning of a uri - they merely act as a conduit through which the creator of a resource (a human naming authority) can associate representations with the semantics identified.
A resource does not always map to a singular file, but all resources that are not static are derived from some using other resources, and by following the derivation tree an author can eventually find all of the source resources that must be edited in order. These same principles apply to any form of derived representation, whether it be from content negotiation, scripts, servlets, managed configurations, versioning, etc. The resource is not the storage object. The resource is not a mechanism that the server uses to handle the storage object. The resource is a conceptual mapping - the server receives the identifier (which identifies the mapping) and applies it to its current mapping implementation (usually a combination of collection-specific deep tree traversal and/or hash tables) to find the currently responsible handler implementation and the handler. All of these implementation-specific issues are hidden behind the web interface; their nature cannot be assumed by a client that only has access through the web interface. For example, consider what happens when a web site grows in user base and decides to replace its old Brand X server, based on an xos platform, with a new Apache server running on Freebsd. The disk storage hardware is replaced. The operating system is replaced.
Information hiding is one of the key software engineering principles that motivates the uniform interface of rest. Because a client is restricted to the manipulation of representations rather than directly accessing the implementation of a resource, the implementation can be constructed in whatever form is desired by the naming authority without impacting the clients that may use its representations. In addition, if multiple representations of the resource exist at the time it is accessed, a content selection algorithm can be used to dynamically select a representation that best fits the capabilities of that client. The disadvantage, of course, is that remote authoring of a resource is not as straightforward as remote authoring of a file. 6.2.3 Remote authoring, the challenge of remote authoring via the web's uniform interface is due to the separation between the representation that can be retrieved by a client and the mechanism that might be used on the server to store, generate, or retrieve the content. An individual server may map some part of its namespace to a filesystem, which in turn maps to the equivalent of an inode that can be mapped into a disk location, but those underlying mechanisms provide a means of associating a resource to a set. Many different resources could map to the same representation, while other resources may have no representation mapped at all. In order to author an existing resource, the author must first obtain the specific source resource uri: the set of uri that bind to the handler's underlying representation for the target resource.
Distinguished, evaluation, factorisations
Second, there exist many addresses that corresponded to a service rather than a document - authors may be intending to direct readers to that service, rather than to any specific result from a prior access of that service. Finally, there exist addresses that do not correspond to a document at some periods of time, such as when the plan document does not yet exist or when the address is being used solely for naming, rather than locating, information. The definition of resource in rest is based on a simple premise: identifiers should change as infrequently as possible. Because the web uses embedded identifiers rather than link servers, authors need an identifier that closely matches the semantics they intend by a hypermedia reference, allowing the reference to remain static even though the result of accessing that reference may change over time. Rest accomplishes this by defining a resource to be the semantics of what the author intends to identify, rather than the value corresponding to those semantics at the time the reference is created. It is then left to the author to ensure that the identifier chosen for a reference does indeed identify the intended semantics. Defining resource such that a uri identifies a concept rather than a document leaves us with another question: how does a user access, manipulate, or transfer a concept such that they can get something useful when a hypertext link is selected?
Rest answers that question by defining the things that are manipulated to be representations of the identified resource, rather than the resource itself. An origin server maintains a mapping from resource identifiers to the set of representations corresponding to each resource. A resource is therefore manipulated by transferring representations through the generic interface defined by the resource identifier. Rest's definition of resource derives from the central requirement of the web: independent authoring of interconnected hypertext across multiple trust domains. Forcing the interface definitions to match the interface requirements causes the protocols to seem vague, but that is only because the interface being manipulated is only an interface and not an implementation. The protocols are specific about the intent of an application action, but the mechanism behind the interface must decide how that intention affects the underlying implementation of the resource mapping to representations.
In other words, rest is optimized for the common case so that the constraints it applies to the web architecture will also be optimized for the common case. Uniform Resource Identifiers (URI) are both the simplest element of the web architecture and the most important. Uri have been known by many names: www addresses, Universal Document Identifiers, Universal Resource Identifiers 15, and finally the combination of Uniform Resource locators (URL) 17 and Names (URN) 124. Aside from its name, the uri syntax has remained relatively unchanged since 1992. However, the specification of Web addresses also defines the scope and semantics of what we mean by resource, which has changed since the early web architecture.
Rest was used to define the term resource for the uri standard 21, as well as the overall semantics of the generic interface for manipulating resources via their representations. 6.2.1 Redefinition of Resource, the early web architecture defined uri as document identifiers. Authors were instructed to define identifiers in terms of a document's location on the network. Web protocols could then be used to retrieve that document. However, this definition proved to be unsatisfactory for a number of reasons. First, it suggests that the author is identifying the content transferred, which would imply that the identifier should change whenever the content changes.
Fielding, dissertation : chapter 6: Experience and, evaluation
The first edition of rest was developed between October 1994 and August 1995, primarily as a means for communicating Web concepts as we wrote the http/1.0 specification and the initial http/1.1 proposal. It was iteratively improved over the next five years and applied to various revisions and extensions of the web protocol standards. Rest was originally referred to as the "http object model but that name would often lead to misinterpretation william of it as the implementation model of an http server. The name "Representational State Transfer" is intended to evoke an image of how a well-designed Web application behaves: a network of web pages (a virtual state-machine where the user progresses through the application by selecting links (state transitions resulting in the next page (representing the. Rest is not intended to capture all possible uses of the web protocol standards. There are applications of http and uri that do not match the application model of a distributed hypermedia system. The important point, however, is that rest does capture all of those aspects of a distributed hypermedia system that are considered central to the behavioral and performance requirements of the web, such that optimizing behavior within the model will result in optimum behavior within the.
At the time, the web's architecture was described by a set of informal hypertext notes 14, two early introductory papers 12, 13, draft hypertext specifications representing proposed features for the web (some of which had already been implemented and the archive of the public www-talk. Each of the specifications were significantly out of date when compared with Web implementations, resume mostly due to the rapid evolution of the web after the introduction of the mosaic graphical browser ncsa. Several experimental extensions had been added to http to allow for proxies, but for the most part the protocol assumed a direct connection between the user agent and either an http origin server or a gateway to legacy systems. There was no awareness within the architecture of caching, proxies, or spiders, even though implementations were readily available and running amok. Many other extensions were being proposed for inclusion in the next versions of the protocols. At the same time, there was growing pressure within the industry to standardize on some version, or versions, of the web interface protocols. The W3C was formed by berners-lee 20 to act as a think-tank for Web architecture and to supply the authoring resources needed to write the web standards and reference implementations, but the standardization itself was governed by the Internet Engineering Taskforce. Org and its working groups on uri, http, and html. Due to my experience developing Web software, i was first chosen to author the specification for Relative url 40, later teamed with Henrik frystyk nielsen to author the http/1.0 specification 19, became the primary architect of http/1.1 42, and finally authored the revision of the.
the dissertation is graded, the postgraduate student must be reserved the opportunity to write a rejoinder to the statements. The faculty council will grade the dissertation on the basis of these statements. Fielding Dissertation: chapter 6: Experience and evaluation. Top, prev, next, since 1994, the rest architectural style has been used to guide the design and development of the architecture for the modern Web. This chapter describes the experience and lessons learned from applying rest while authoring the Internet standards for the hypertext Transfer Protocol (http) and Uniform Resource Identifiers (uri the two specifications that define the generic interface used by all component interactions on the web, as well. As described in Chapter 4, the motivation for developing rest was to create an architectural model for how the web should work, such that it could serve as the guiding framework for the web protocol standards. Rest has been applied to describe the desired Web architecture, help identify existing problems, compare alternative solutions, and ensure that protocol extensions would not violate the core constraints that make the web successful. This work was done as part of the Internet Engineering Taskforce (ietf) and World Wide web Consortium (W3C) efforts to define the architectural standards for the web: http, uri, and html. My involvement in the web standards process began in late 1993, while developing the libwww-perl protocol library that served as the client connector interface for momspider.
The opponent must come from outside the restaurant University of Eastern Finland and be at least a docent or hold a corresponding scientific qualification. A person cannot be appointed as an opponent if he/she has written publications or participated in research projects with the postgraduate student during the student's postgraduate studies or if he/she is otherwise disqualified. The faculty representative must hold at least a doctoral degree in the same or related subject. The representative familiarises him/herself with the dissertation and observes the public examination. After the public examination, the custos, the opponent(s) and the faculty representative hold a meeting to discuss grading. The custos then writes a statement about the proceedings of the public examination. After the public examination, both the opponent(s) and the faculty representative write a statement about the dissertation and the public examination.
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Evaluation of a doctoral Dissertation, before evaluation the doctoral dissertation must be tested in electronic plagiarism detection system Turnitin. The doctoral candidate applies for permission to defend his/hers doctoral dissertation in public by filling a form and gives in the dissertation manuscript in one pdf-document to the address: FiloDoctoralstudies(at the dean appoints, on make the basis of the proposal made by the head of School. They are chosen, if possible, from outside the student's faculty. The supervisor cannot be one of the examiners. Furthermore, a person cannot be appointed as an examiner if he/she has written publications or participated in research projects with the postgraduate student during the student's doctoral studies or if he/she is otherwise disqualified. The dean decides on giving the doctoral candidate permission for public examination on the basis on the preliminary examiner's statements and the candidate's possible rejoinder. The doctoral dissertation is graded by the faculty council after the public examination. The dean appoints, on the basis of the proposal made by the head of School, one or two opponents, a chairman of the public examination (a custos and a faculty representative to grade the dissertation.