Introduction
The semantic web is a network of data that allows data to be shared, not just by application constraints.
But the semantic web is not just about putting data on the internet, but about trying to connect it and generating data that is connected to real things so that people and machines can read and understand the data.
The semantic web isn ' t just about putting data on the web. It is about making links, so this a person or machine can explore the web of data.
--linked Data Design Issues. Tim Berners-lee
Linked data is the first feasible form of semantic web representation, using the RDF data model, which uses the URI (Uniform Resource Identifier) to name the data entity to publish and deploy the instance data and the class data, so that the data can be revealed and retrieved through the HTTP protocol. At the same time, it emphasizes the interrelated and interrelated information of data, and it is beneficial to the understanding of human computer.
Linked data is a set of best practices for publishing and deploying instance and class data using the RDF data model, and Uses Uniform Resource Identifiers (URIs) to name the data objects. The approach exposes the data for access via the HTTP protocol, while emphasizing data interconnections, interrelationship S and context useful to both humans and machine agents.
--linked Data FAQ. M.K. Bergman
Because the semantic web is a huge project, accompanied by various difficulties to make it a long-term goal and vision, and relational data is a kind of practical activities, it is feasible and practical, become the current semantic Web implementation of a best feasible solution.
the characteristics of RDF
The Resource Description Framework (Resource Description framework), as a derived version of XML (extensible Markup Language), is the basic data model for associated data. Tim Berners-Lee (Tim Berners-lee) faced the following two questions when designing it:
• How to design languages that are easy to learn and easy to spread and suitable for standardization?
• How to design the import and export of discrete data?
To address these two issues, RDF has some of the following features:
• Use XML as the base language
• Use URIs as the name of the real thing
• Use HTTP URIs to make people know how to find data in a network by name (that is, create discrete data portals)
• Contains links to other URIs that allow people to find more useful things (i.e., create discrete data exits)
• Storing data using ternary (Triple) forms
In fact, some versions of RDF are not in the XML language, and this is basically the original version.
A simple example of RDF
Copy Code code as follows:
<?xml version= "1.0"?>
<RDF:RDF xmlns:rdf= "http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:dc= "HTTP://PURL.ORG/DC/ELEMENTS/1.1/" >
<rdf:description rdf:about= "http://www.w3.org/" >
<dc:title>world Wide Web consortium</dc:title>
</rdf:Description>
</rdf:RDF>
Using the RDF example through the RDF authentication Service, the following list appears:
Triples of the Data Model
| Number |
Subject |
predicate |
Object |
| 1 |
http://www.w3.org/ |
Http://purl.org/dc/elements/1.1/title |
"World Wide Web Consortium" |
What is this stuff?
Ternary group (Triple), the basic representation unit of the RDF data model. The so-called ternary group is: the Main (Subject)-predicate (predicate)-Bing (object).
A Triple Store is designed to store and retrieve identities this are constructed from triplex collections of strings (sequ Ences of letters). These triplex collections represent a subject-predicate-object relationship, or less to the corresponds n put forth by the RDF standard.
--triple Store. Jack rusher.
Unlike relational data, the data itself does not have a huge connection (which is not feasible in the face of such a large data network), but rather uses a human statement (Statement) to store data, for example:
Tom is a mans. (Tom is a man)
Tom lives in a red house. (Tom lives in a scarlet room)
Tom married with Lili. (Tom and Lili are married)
It can be seen that the ternary form also has powerful data storage expression potential, which is the long-term beneficiary of this form. Of course, as the above statement is friendly to humans, but not very friendly to the machine, because the predicate is not well qualified for the object, at least the machine does not think so. So we should write a pattern like this:
Tom (Tom) Sex (Sex) man (male)
Tom (Tom) House (home) Red (red)
Tom (Tom) wife (wife) Lili (Lili)
Back to the title, what is this stuff? It expresses the following elements:
1.http://www.w3.org (indicates that the statement is the subject of the description, as the HTTP URI maps the real thing, so it can be seen as a description of what the real thing is)
2.http://purl.org/dc/elements/1.1/title (the property of the subject, generally representing the type of the object, for example, Dc:title is the name of the resource used in the Dublin core, i.e. the object is a name for the resource).
3.World Wide Web Consortium (object)
How do people get RDF?
The following illustration illustrates this process:
• First the HTTP URI is requested.
• Usually the browser HTTP request header is: text/html, application/xhtml+xml type, so the server returns the general html/xhtml document.
• But for the Semantic browser, its HTTP request header is: Application/rdf+xml type, so the server for 303 redirect, get the corresponding RDF file.
That is, you can return two forms of expression for an HTTP URI: document and data. This creates two different networks, one for human reading and the other for machine-readable data networks.
