Several researchers have proposed a multilevel database approach to organizing Web-based information. The main idea behind these proposals is that the lowest level of the database contains primitive semi-structured information stored in various web repositories, such as
hypertext documents. At the higher level(s) meta data or generalizations are extracted from lower levels and organized in structured collections such as relational or object-oriented databases.
Web Query Systems
There have been many web-base query systems and languages developed recently that attempt to utilize standard database query languages such as SQL, structural information about web documents, and even natural language processing for accommodating the types of queries that are used in World Wide Web searches. We mention a few examples of these Web-base query systems here. W3QL combines structure queries, based on the organization of hypertext documents, and content queries, based on information retrieval techniques. WebLog is a logic-based query language for restructuring extracted information from Web information sources. Lorel and UnQL support querying of heterogeneous and semi-structured information on the Web using a labeled graph data model. TSIMMIS helps to extract data from heterogeneous and semi-structured information sources and correlates them to generate an integrated database representation of the extracted information.
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