This article describes the XML binding RDF implementation Web data based on semantic description. Today, more and more web applications need to be interoperable by exchange data. The appearance of XML enables syntax interoperability between the implementation web application, and RDF can achieve semantic interoperability between web applications by using XML. So how do XML and RDFs do their respective functions? Introduction - What is the semantic semantics? This is a problem that is more difficult to answer, just like someone asks Ontology what to do. If the reader has some understanding of the semantic web, it will know that the semantics is a key element that is changing the Internet, or even an important element of improving the efficiency of global economic development [1]. This article is not an exact explanation to give semantics, because this is really difficult, especially when this concept is quoted by different fields, it often has some differences. The purpose of discussing semantics is to better understand what role in XML and RDF in the data representation and exchange, more clearly see the difference between XML and RDF, respective advantages and deficiencies. We can simply see semantic as the meaning of the concept represented by data (symbol), and the relationship between these meanings is a logical representation of the abstraction or higher level of data. For computer, semantics generally refer to the user's approach to computers used to describe the real world, that is, the user is used to contact the computer to represent and reality the world. Perhaps this is still not a popularity, let us further explain the meaning of semantics through an example: Taking the relational database as an example, the data in the database can be simply considered to be stored in a sheet, such as our basic information of the students. Enter a "Student" table. At this time, the collection of each column data in the table is implied in the corresponding concept to be expressed by the column data. This concept is often reflected in the designer's attribute corresponding to the column data. Name, such as "Name", "Sex", etc. The relationship between these attributes is equivalent to the relationship between the concepts of the data, which are the properties of this entity. Attributes and relationships in the database table can be regarded as semantic information for data. Of course, semantics are not as simple, and its representation may be more complex, even more than the expression of database modeling languages such as E-R model. In fact, semantics are not introduced into the new concept of IT field. The database has long been distinguished by semantics, and as part of database modeling, query, and transaction management technology, semantics is to ensure that data management systems achieve scalability, A key element for efficiency and robustness requirements. The syntax and semantics in the data representation have learned what is semantic, let us further discuss the role of grammar and semantics in data descriptions and exchanges. In fact, the true purpose to be achieved by data exchange is to obtain the meaning representing the exchanged data, and implement the exchange of data in the meaning of the data, not the exchange of simple data itself, this is similar to the information exchange between people. For humans, we can interact with the same language, and the interaction between the language organization (equivalent to grammar) (equivalent to the syntax) in the language organization (equivalent to syntax) to make the other party to understand. The communication between people and people does not require a very stringent grammar, even if the other party has a certain mistake in language expression, we may still understand the meaning of the other party to express. However, for information exchange between computers, the syntax and semantics are not available. The correct syntax expression is the premise of ensuring information exchange and processing between the computer, and the data semantic description is the basis for the correct understanding and reasoning of the computer.
For most of today's computer applications, the information generated does not use a unified grammatical description format, and the information has thousands of differences in grammatical description, which causes the syntax heterogenesis of information expressions; The explanation of the meaning (ie, the semantics) is written in a hard code, and the information semantic model mode method of the so-called program semantics [2], the syntax of the semantics and information of the information is separated. Description, the understanding of the information is cured into a particular code logic. Therefore, the systematic semantics have a large limit, neither extensibility does not have versatility, difficult to maintain and integrate. In contrast to the program semantic information modeling method, the declarative semantic modeling method [2] is incorporated into the data layer by separating the semantic description of the data with the specific application logic, and the interpretation of the semantics Give a general-purpose formal system (such as first-order logic, description logic, Datalog and other reasoning systems), and has very good adaptability, reusability of specific data and application logic. Data-based description is to describe the semantics of data in a declarative semantic modeling method. The pressure of the application processing data can be greatly reduced by the semantic description of data. XML - Web data syntax description standard information is different in grammatical description, and we can use the necessary data format to convert information into target applications that can process syntax formats. Of course, more ideal cases should be that all information uses the same syntax to describe that the emergence of XML makes different types of data to be possible in the same format. XML has become an actual criterion for data representations and exchanges on the web, which is an effective way to share data between applications or between the machines. The development of XML and its related technologies greatly promotes the unity of syntax description in information expression and exchange process, and more and more applications start using XML as its data, configuration information, message, and service syntax description mode. To date, XML has become the most ideal data expressions on the web. XML scalability is the most basic feature of XML distinguishably other tag language. The core of XML is to establish the structure of the data represented by a standardized manner, and the definition of the specific mark is left to the user. XML scalability enables XML to meet the needs of various domain data descriptions and can encode any data exchanged between computers. Whether the XML is already enough when we just contact XML, we may be excited because XML's performance, scalability, and bright prospects, but follow the problem: two messages or data represented by XML, How can I exchange? Is it that we use an XML format, and the exchange is good. In addition to providing us with a format that can be applied automatically, XML does not further facilitate the degree of automation of data exchange, we also need to interpret XML data through a dedicated program to obtain the data part of the target application. . Note that the explanations here are different from parsing of XML documents. Of course, the premise of explaining the XML document is the first analysis of the XML document. Although XML already has a variety of parsers, the true role of the parser is an XML read and processor, not an interpreter. Therefore, we must use a specific application to interpret the content of XML, it is clear that there is no interchangeability and versatility between these programs. Although the flexibility of XML allows users to quickly and easily describe any content, due to XML does not explain its tag meaning, most processing applications require these tags to meet some standards or both parties. XML allows users to define collections of these tags via XML mode. XML mode (such as XML DTD and XML Schema et al.) Provides a constraint mechanism for XML documents to limit the structure relationship between the tags used in the XML document and these tags.
The XML mode provides a certain semantic description ability for XML documents, but the semantics of the XML mode are still implicit. Elements of XML mode Emissive Emissions either by the user inference according to the name of the element (by natural language description), either by another document, the XML mode does not explain the semantics contained therein. In order to implement an interpretation or conversion of an XML document, the user must encode these semantics into the tool, and the final interpretation of the data is left to a particular application. Not only that, since the XML mode can only be verified for the syntax of XML, it cannot distinguish between XML attributes and elements in meaning, so we can map them into a variety of different XML structures for the same information. For example, we must explain which writer (Name) of a book (Author) is a definition of a variety of XML Schema in Example 1. Example 1 DTD definition corresponding to multiple XML Schema's definition of XML instances for the same information
This uniqueness of this data expression means that there are a variety of different interpretations, and the same applications may also make the same explanation of different XMLs. This explanation has a multi-to-many relationship such that we must agree on the name, organizational format, and meaning of the tag used to be used before switching the XML document. Any unilateral extension of the XML document may give the data. The exchange process brings more trouble and even leads to failure. However, this way of implementing information sharing through the convention is only applicable to information exchange between two or two, but does not meet a wide range of users or groups of information on the Web. Suppose we want to integrate the XML information generated by n applications, even if the meaning of integrating parts is exactly the same, because they come from different applications, their respective XML mode descriptions are likely to have different (including the difference between marking naming). The inconsistency on the structural organization), so we still have to do a large number of modes between modes, while the purpose is to ensure that they are maintained at the description of the grammar. Of course, we can describe all relevant XML information by adopting a unified global XML mode, but this is obviously unrealistic, even in an enterprise, we also have a stable standardized enterprise data representation mode. RDF (Resource Description Framework) - Semantic Description Model RDF is the abbreviation of Resource Description Framework, ie resource description framework. RDF is an XML application for processing metadata. The so-called metadata is "data of data" or "information describing information". Perhaps this interpretation of the metadata is unbearable, a simple example, the content of the book is the book's data, and the author's name, the address or copyright information of the publishing house is the metadata of the book. The division of data and metadata is not absolute, and some data can be used as data processing, or as a metadata processing, for example, the author's name can be used as data instead of metadata processing. It is well known that the description of resources is related to the field and applications, such as the description of a book and a description of a Web site, that is, different vocabulary needs to take different resources. Therefore, the RDF specification does not define the vocabulary used by the description of resources, but defines some rules, which must be followed when the fields and applications define the vocabulary used to describe resources. Of course, RDF also provides basic vocabulary when describing resources. Through RDF, people can use their vocabulary to describe any resources, but people are more happy to describe it to describe Web sites and pages, because the use of structured XML data, search engines can understand the precise meaning of metadata, make search Be more intelligent and accurate, you can avoid the current search engine often returns the unrelated data. Of course, the premise is that RDF and standardized RDF vocabulary are widely used on the Web, and the search engine needs to understand the use of the glossary. Simply, an RDF file contains multiple resource descriptions, and one resource description consists of a plurality of statements, and a statement is a three-element composed of a resource, attribute type, attribute value, indicating an attribute of the resource. The statement in the resource description can correspond to the statement of the natural language, the resource corresponds to the subject in the natural language, the attribute type corresponds to the predicament, the attribute value corresponds to the object. Since the statement of the natural language can be sentenced, the previous simple correspondence is only a problem that exists than XML, because XML does not have semantic description capabilities. To this end, W3C recommends Semantic Limitations of XML in RDF (Resource Description Framework) standards. RDF proposes a simple model to represent any type of data. This data type is composed of a tagged connection arc between nodes and nodes. The node is used to represent resources on the Web, and the arc is used to represent the properties of these resources.
Therefore, this data model can be convenient to describe objects (or resources) and their relationships. The data model of RDF is essentially a binary relationship. Since any complex relationship can be broken down into multiple simple binary relationships, the RDF's data model can be used as the basics of any other complex relationship model. RDF and XML are complementary. First, RDF wants to specify the semantics of XML in a standardized, interoperable manner. XML documents can be referenced to RDF by simple way. As shown in Example 2. Example 2 XML reference example of RDF
XMLns = "http://www.w3.org/tr/wd-rdf-syntax#" About = "http://www.w3.org/test/page" S: author = "http://www.w3.org/staff/ora" />
