[Distributed computing environment learning notes] 7. Semantic Web

Author: gnuhpc
Source: http://www.cnblogs.com/gnuhpc/

1. Features of Semantic Network:

Each resource has a clear definition, such as software, files, people, and locations. There is a clear definition of the relationship between concepts, such as software-generated files, software dependent on software, file versions, files with themes, location points. The goal is to automatically process information. It provides intelligent services such as information proxy, search proxy, and information filtering. The intelligent services provided by semantic web should surpass the technical level of these services and overcome the limitations that they can only run independently and cannot interact with each other. The technical basis of Semantic Network is XML and RDF. The basic implementation method is to develop a formal information protocol language with enhanced features to uniquely determine the meaning of information, its ultimate goal is to become the infrastructure for intelligent network services and application development, and become a media for machine-to-human collaboration.

 

2. Target of Semantic Network:

Enable computers to "understand" the information and knowledge distributed on the Internet, and better process and utilize the information and knowledge on the premise of "Understanding, make web an intelligent information service platform that supports global knowledge sharing and provide excellent services to people.

3. Semantic Network Problems

Information Retrieval-Keyword retrieval and content-based retrieval
Information Extraction-Metadata: data related to data. It mainly includes

• Syntax metadata: Describes non-context information about data content. Such as the document size, position, and creation date
• Structure metadata: provides information about the content structure. For example, you can use a DTD or XML schema to define elements, attributes, and entities used in an XML document, and relationships between different elements and attributes.
• Semantic metadata: Links, rules, and constraints are added to the syntax and structure metadata.

Information Representation-separation of content and representation
Information and natural language semantics
Data Mining and Knowledge Discovery
Information Integration and concept Integration

4. Semantic Network Layer

In this system, Unicode, Uri, XML, RDF, ontology, logic, proof, and trust

• The Unicode and Uri of the first layer. This layer is the basis of the entire semantic web, where Unicode processes resource encoding and Uri identifies resources
• Layer 2 XML + NS + XML schema, used to represent the data content and structure
• The third-layer RDF + RDF Schema, used to describe resources on the web and their types
• Layer-4 ontology vocabulary, used to describe the connections between various resources
• Layer 5 to Layer 7 are logical reasoning operations on the basis of Layer 4 below, including Principle and reasoning rules, authentication mechanisms and trust mechanisms
• The core layer is XML, RDF, and ontology, which are used to represent the semantics of Web Information.

5. RDF

The Resource Description Framework (RDF) provides a general framework for expressing this information and enabling it to exchange between applications without losing semantics. RDF is a language used to describe resources. It is a standard recommended by W3C to describe metadata on the web. A Web identifier (URI) is used to identify a transaction, and a simple property and attribute value are used to describe a resource.

It consists of three parts:

• RDF Model
• RDF/XML syntax
• RDF Schema

TriplesIt is defined as (subject, predicate, object). It consists of three parts: subject (thing), predicate (attribute), and object (value. The type of subject and predicate is Uri, indicating a web resource. The object can be URI or literal. The triples of RDF are also known as the statement ).

The graph model of RDF:The RDF declaration can be expressed as a directed, labeled graph.

• An Elliptical node represents the subject and object referenced by a URI.
• The box node indicates the object of the text type.
• Indicates the predicate referenced by Uri.

 

RDF/XML Syntax:

It is used to represent and exchange RDF graphs. For example

• Specify an empty node identifier for all empty nodes in the RDF diagram.
• Generates an RDF: Description element corresponding to the subject in each RDF triples.
• Multiple declarations of the same subject can be combined into an RDF: Description element.

RDF Schema:Extended to RDF, which can be used to describe and define classes and attributes related to a specific application, so as to create a custom vocabulary, such as a dictionary Expression Language.

Functions of RDFS:

• Define the categories of resources and attributes;
• Define the types of resource classes and attribute values applied to properties;
• Define the syntax of the above class declaration;
• Declares attribute classes of metadata standards defined by other organizations or organizations.

Description of the RDF class

• A class refers to the type or category of a thing. RDF: Class, RDF: Resouce, RDF: type, and RDF: subclassof
  For example:
• Description of the RDF attributes, such as RDF: property, RDF: range, and RDF: domain.
  For example:

Semantic Web and semantic web service. The difference is like the difference between Web Service and Web Service. Semantic Web provides a semantic web network, while Semantic Web Service further provides support for external interface calls.

6. Ontology

A systematic explanation or explanation of objective existence is concerned with the abstract nature of objective reality. An ontology is a formal, explicit specification of a shared conceptualization-Gruber

• 'Conceptualization' refers to the model obtained by abstracting concepts related to phenomena in the objective world.
• 'Explicit' refers to the concepts used and the constraints for using these concepts.
• 'Formal' indicates that ontopology is readable by computers.
• 'Shared 'refers to the knowledge that is recognized together in ontopology, and reflects the concept set recognized in related fields.
• "Sharing" refers to the knowledge that is recognized together in ontology and reflects the concept set recognized in the relevant fields.
• "Conceptual model" refers to a model created by abstracting concepts related to phenomena in the objective world
• "Explicit" means that the concepts used and the constraints for using these concepts are clearly defined.
• "Formalizing" indicates that ontology is readable and understandable by computers.

Modeling metadata:

Class or concept (concepts): refers to any transaction, such as a job description, function, behavior, strategy, and reasoning process. In terms of semantics, it represents a set of objects. Its definition generally uses a frame structure, including the name of a concept and a set of relationships between concepts and other concepts, and the description of the concept in natural language, e.g. in university-ontology: Student and Microsoft sor are two classes

Relations: interaction between concepts in a field. formally defined as a subset of n-dimensional cartesian products: R: C1 × C2 ×... × CN such as: subclass-of, is-

Functions: a special type of relationship. The first n-1 elements of the relationship can uniquely determine the nth element. Formally defined as F: C1 × C2 ×... * CN-1 → CN. For example, mother-of is a function. Mother-of (x, y) indicates that Y is the mother of X.

Axioms: represents Yongzhen's assertions. For example, concept B belongs to concept.

Instance: represents an element. In terms of semantics, instances represent objects. Such as: student called Peter is the instance of student class.

Four basic relationships:

Construct ontology rules:

• Clarity and objectivity: ontology should use natural language to provide clear and objective semantic definitions for defined terms
• Completeness: The given definition is complete and can fully express the meaning of the term described.
• Consistency: inferences drawn from terms are compatible with the meaning of the terms themselves, and there is no conflict
• Maximum monotonous Scalability: you do not need to modify the existing content when you add General or dedicated terms to ontopology.
• Minimum commitment: Give as few constraints as possible to modeling objects

Widely used ontology:

Language Stack:

 

6. Semantic Web Applications

• Semantic Web Services)
• Content/knowledge management)
• Concept searching)
• Intelligent Agent)
• Universal computing (ubiquitous/pervasive computing)

 

Author: gnuhpc
Source: http://www.cnblogs.com/gnuhpc/