Web semantics

The implementation of the Semantic Web is based on the XML (eXtensible Markup Langauge) language and Resource Description Framework (RDF). . XML is a tool for defining markup languages, which includes XML declarations, DTD (document type declaration) to define the language syntax, detailed descriptions of markup, and the document itself. Markup and content. RDF is used to express the content of the web page.

Resource Description Framework

RDF (Resource Description Framework) is a language specification recommended by W3C for describing information resources on the WWW and the relationships between them. .

RDF(S) is an important part of the Semantic Web. It uses URI to identify different objects (including resource nodes, attribute classes or attribute values) and can connect different URIs to clearly express the relationship between objects. Relationship.

Implementation

Although the Semantic Web is a better network, its implementation is a complex and vast project. At present, the architecture of the Semantic Web is under construction, and it mainly requires support from the following two aspects:

That is: through a unified and complete set of data standards for the network Information is marked more thoroughly and in detail, enabling the Semantic Web to accurately identify information and distinguish its role and meaning. To make Semantic Web searches more precise and thorough, making it easier to determine whether information is true or false, and thus achieving practical goals, we first need to develop standards that allow users to add metadata (i.e., tags with detailed explanations) to web content and enable users to Specify exactly what they are looking for; then, find a way to ensure that different programs can share content from different sites; and finally, ask users to add additional functionality, such as adding applications.

The implementation of the Semantic Web is based on the XML (eXtensible Markup Langauge) language and the Resource Description Framework (RDF). XML is a tool for defining markup languages. Its content includes XML declarations, DTD (document type declaration) to define the language syntax, detailed descriptions of markup, and the document itself. The document itself contains markup and content. RDF is used to express the content of web pages.

If the data network can be realized through hundreds of millions of individuals in a short time, then the semantic intelligence of the network must be achieved through the cutting-edge human intelligence group efforts to achieve. The development of an information search engine with semantic analysis capabilities will become the most important step in the Semantic Web. This engine can understand human natural language and has certain reasoning and judgment capabilities.

Semantic search engine (semantic search engine) and search engine with semantic analysis capabilities (semantically enabled search engine) are two different things. The former is just the use of the semantic network, a way of information search, while a search engine with semantic analysis capabilities is a type of search engine that can understand natural language and further provide answers that are more in line with the user's psychology through computer reasoning.

Prospects

The architecture of the Semantic Web is under construction. The current international research on this architecture has not yet formed a satisfactory and rigorous logical description and theoretical system. , Chinese scholars have only made a brief introduction to this system structure based on foreign research, and have not yet formed a systematic explanation.

The implementation of the Semantic Web requires the support of three key technologies: XML, RDF and Ontology.

XML (eXtensible Marked Language, i.e. extensible markup language) allows information providers to define tags and attribute names according to their needs, so that the structure of the XML file can be complex to any extent.

It has the advantages of good data storage format and scalability, high structure and easy network transmission, coupled with its unique NS mechanism and multiple data types and verification mechanisms supported by XML Schema , making it one of the key technologies of the Semantic Web.

The current discussion on the key technologies of the Semantic Web mainly focuses on RDF and Ontology.

RDF is a language specification recommended by the W3C organization for describing resources and the relationships between them. It has the characteristics of simplicity, easy expansion, openness, easy exchange and easy synthesis.

It is worth noting that RDF only defines how to describe resources, but does not define what data is used to describe resources. RDF consists of three parts: RDF Data Model, RDF Schema and RDF Syntax.

1. The Semantic Web expands the existing Internet and adds content that expresses its meaning to information, allowing computers to automatically work together with people. In other words, the various resources in the Semantic Web are no longer just various connected information, but also include the true meaning of the information, thereby improving the automation and intelligence of computer processing of information. Of course, computers do not have real intelligence. The establishment of the Semantic Web requires researchers to effectively represent information and formulate unified standards so that computers can effectively and automatically process information.

(Source: He Bin and Zhang Lihou "Information Management Principles and Methods" Tsinghua University Press, second edition, July 2007)

Semantics Network architecture

• The first layer: Unicode and URI are the basis of the entire architecture.

• The second layer: XML+NS+XMLSchema, which is responsible for grammatically representing the content and structure of data. It separates the representation form, data structure and content of network information by using a standard format language. .

• The third layer: RDF+RDF Schema, which provides a semantic model for describing information and types on the Internet. Among them, RDF (Resource Description Framework), the resource description framework, is a language specification recommended by W3C for describing information resources on the WWW and the relationships between them. RDF(S) is an important part of the Semantic Web. It uses URIs to identify different objects (including resource nodes, attribute classes or attribute values) and can connect different URIs to clearly express the relationship between objects.

• The fourth layer: ontology vocabulary layer. Ontology is a clear specification for the conceptualization and formalization of domain knowledge. In the semantic web architecture, the role of ontology is mainly reflected in: (1). Concept description, that is, domain knowledge is revealed through concept description; (2). Semantic disclosure, ontology has stronger expression ability than RDF and can reveal more Rich semantic relationships; (3). Consistency. As a clear specification of domain knowledge, ontology can ensure semantic consistency, thereby completely solving the phenomenon of polysemy, multiple words with one meaning and ambiguous word meanings; (4). Reasoning support , The ontology’s certainty in concept description and its powerful semantic revealing ability effectively ensure the effectiveness of reasoning at the data level.

• The fifth layer: Logic layer, responsible for providing axioms and reasoning principles, providing the basis for intelligent services. Among them, description logic (DescriptionLogic) is a formalization of object-based knowledge representation. It absorbs the main idea of ​​KL-ONE and is a decidable subset of first-order predicate logic. It is different from first-order predicate logic in that the description logic system can provide decidable reasoning services. In addition to knowledge representation, description logic is also used in many other fields. It is considered to be the most important normalized form of object-centered representation language. An important feature of description logic is its strong expressive ability and decidability, which ensures that the inference algorithm can always stop and return the correct result. Among the many formal methods of knowledge representation, description logic has received special attention for more than ten years. The main reasons are that: they have clear model-theoretical mechanisms; they are very suitable for representing application fields through concept taxonomy; and they provide A very useful reasoning service.

• The sixth layer of certification layer and the seventh layer of trust layer are responsible for providing authentication and trust mechanisms.

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