Delight in Thinking

This topic is very luxurious, encompasses many of the current hot area of information technology terms, from Web2.0 to cloud computing, these terms constitute a bright Web world from the past into the future road map.

The life cycle network around the world is a stage of ten years, from the first generation Web experiences to Web2.0 about 10 years, 10 years, Web address of the person's interaction with the network problems, from Web1.0 Just read the network information to provide users the convenience to the development of Web2.0 to provide users with interactive access, from, Web is not just a media, but rather an information exchange platform to communicate with each other. In the Web2.0 environment, users do not just Web-readers, but also Web content providers and participants, today, Web2.0 basic Web has matured and become mainstream. Web2.0 site full of large networks, and nurture a large number of users, it can be said, Web2. Really fostered the rise of a virtual network society.

W eb2.0 A key feature is involved, that Web users can participate in Web content development. This is a surface feature, in this feature is the technical architecture behind the changes, Web1.0 is mainly a web form, but to the Web2.0, HTML is no longer a Web-based application system but, in particular, is called of the content management system (CMS) for Web applications, Web1.0 to Web2.0 development is from the Web Page to Web Application Development Changes.

This kind of structural change in technology has changed the basic properties of networks, Web is no longer an isolated site were linked through the network, but a variety of Web application integration, Web content into functional and integrating through a whole into a large system. In order to achieve this integration, need to be addressed in the Web environment, communications between systems, particularly the reuse of functions and data problems, the birth of the Web Service framework, such a service-oriented architecture to become a landmark structure Web2.0 . Therefore, from a technical architecture perspective, Web2.0 feature is that Web services Web Service.

W eb as a large distributed system requires not only open the Web Application services (Web applications), also need to be structured description of data. Only through a structured description of data, application systems can be understood, in other words, an effective distributed network applications need to have the machine can understand the data. If Web2.0 is built on open service architecture, then a new generation of networks will be built on the basis of a machine can understand the structured and interrelated with the data environment, once the data environment established, then the Web will enter a new era, this new Web environment, we can call Web3.0.

W eb3.0 to be addressed is a data representation, allows the machine to understand the data structure information, the data structure information is called the semantic information, which is the core of semantic networks need to address the problem, so the Semantic Web can be viewed as is Web3.0 start. Semantic Web has experienced a development from concept to reality the process, its technical architecture has become increasingly clear, that is of concern associated with the data (Linked Data). There are two basic points associated data that describe and connect. Description and links are for machine service, the machine can be achieved by describing the automatic discovery and confirmation of the link can support the machine automatically link.

We go back and look at web1.0, 1.0 conditions, the browser get information from the server directly displayed on the screen, do not know the meaning of information, web pages and link each other through hyperlinks, but the need to manually click the trigger, 2.0 by the machine to automatically aggregate all kinds of information, and to 3.0, the network in the data layer on the establishment of a link mechanism, the data structure information is well described with, and through the URI to ensure that the machine can automatically link to a variety of data, to achieve intelligent automation of information aggregation.

Then, cloud computing is not the natural effect?

L inked data can be the basis for a new generation of Semantic Web has a very broad application prospects. W3C recently announced, SKOS Linked Data will be full of. (Needle, 2009) which is significant for the library community. SKOS of the linked data should benefit from the libraries of the United States Congress, the Library of Congress Subject Headings (Library of Congress Subject Headings) of all the Linked Data, Linked Data application to become a successful example, promoted the Linked Data to practical. This in turn can be said that libraries contribute to the development of the Internet instance.

L inked Data is based on RDF and http protocols, in other words, Linked Data is to pass through the Http RDF data, and the RDF data is a special rule to follow the semantics of data, this rule is that any resources are characterized with a URI. So URI \ RDF \ HHTP constitute the three cornerstones of Linked Data. The application of any Linked Data revolve around these three aspects of the. Such as:

• How to build a resource URI?
• How to create RDF resources?
• How to use http to transfer RDF?
• How to accept and parse RDF data resources? And so on.

L inked Data Application There are two basic models: a model for the browser / server model, that the people via a browser to access Linked Data; The other model is a client / server model, where clients mainly refers to the application system, the model is actually the system and data transfer between systems. Whatever the mode, Linked Data is to pass through Http.

H ttp protocol actually defines two processes, one request, the other is the response. To these two processes as the blueprint, we can simulate a Linked Data transfer process.

• Client-side or browser sends a request to the RDF file server, requests the server to return an RDF document. Send this request is simple, you can directly enter a rdf file suffix, such as http://www.cloudlibrary.info/rainzenfoaf.rdf rdf is a simple request. Of course, this request is very weak, the file suffix is not necessarily with the rdf for RDF format, in turn, RDF format file suffix it may not rdf. So, to pass with the file extension is not very reliable RDF request. What we need is a mandatory request RDF very clear way, this request can only be through the system (such as the browser) rather than be issued manually. Now a common browser can not issue such a request, in order to apply Linked Data RDF we need to send the requested browser.
• RDF when the server receives a request, need to return an RDF document, and inform the client that this is a RDF file. This process is called content negotiation. To achieve this RDF-based content negotiation, which would set the MIMEType, the definition of an RDF type. RDF 2004, one on the content type: Application / RDF + XML to be registered. Linked Data on the terms, content negotiation is very important, if you want to publish Linked Data, require the server can implement content negotiation.
• Device sent a service response to a client, particularly the browser, how to parse the RDF file? Particularly in the browser mode, because RDF is not for seeing, but to the machine to see how the machine language translation of the expression of adults to read? This in turn requires a special browser to parse RDF.

View from the process, applications linked data needs:

• RDF can send a request, and be able to resolve RDF browser, we call RDF browser. Keven described in his blog a lot of RDF browser or plug-ins. (Wei, 2009)
• A server to return RDF type of server. Fortunately, we often use the Apache open source http server: that is one of the few to achieve a good content negotiation server.

Linked Data released in the use of Apache, the need for a simple Apache settings, need to increase the one on RDF's content-type, is set in Apache, or in. Htaccess to add a type description: AddType application / rdf + xml rdf . This Apache receives a request for RDF, RDF type can send messages back.

However, as application / rdf + xml is a new registration, and some browsers do not compatible, I found a phenomenon, visit http://www.cloudlibrary.info/rdf/rainzenfoaf.rdf when the software by checking the file header that, the server returned an application / rdf + xml document, but by Firefox to see the file information, been interpreted as text / html. It seems firefox's default content-type is text / html, and not authorized application / rdf + xml type, when receiving this type, only use the default value.

Another interesting phenomenon is that, Apache's default type is text / plain, if no RDF type, the server can not confirm RDF file to start the default value, the RDF file as text / plain. Return the text file information, then the browser displays the text file. So, is the need to increase application / rdf + xml then this type? Is not necessarily a matter of fact, already stated, FireFox the application / rdf + xml interpreted as text / html, then we add a type: AddType text / html rdf also line, or directly to the Apache's default value is set to text / html on the line. So how do you explain the return to send over the text / html message, the browser was able to resolve it into RDF? It seems that the browser client also needs a judge, by analyzing the markup language to determine whether the RDF file. However, in the communication between systems, I think, or should be enabled application / rdf + xml, so clearly more reliable.

This text is formed during the discussion and Keven, thanks to Keven contribution to this article.

References:

Needle, David. 2009. W3C's New SKOS Standard Advances Linked Data. [Online] August 18, 2009. [Reference date: August 27, 2009.] http://www.internetnews.com/dev-news/ article.php/3835176 .

Wei, Liu keven. 2009. Associated data browser. Number Chart Research Notes. [Online] August 26, 2009. [Reference date: August 27, 2009.] http://www.kevenlw.name/archives / 1844 .

Background Links

http://www.w3.org/Protocols/

http://www.iana.org/assignments/media-types/application/