cs345-5

cs345-5 - 1 Information Integration Mediators...

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Unformatted text preview: 1 Information Integration Mediators Semistructured Data Answering Queries Using Views 2 Importance of Information Integration Very many modern DB applications involve combining databases. Sometimes a database is not stored in a DBMS --- it could be a spreadsheet, flat file, XML document, etc. 3 Example Applications 1. Enterprise Information Integration: making separate DBs, all owned by one company, work together. 2. Scientific DBs, e.g., genome DBs. 3. Catalog integration: combining product information from all your suppliers. 4. Etc., etc. 4 Challenges 1. Legacy databases : DBs get used for many applications. You cant change its structure for the sake of one application, because it will cause others to break. 2. Incompatibilities : Two, supposedly similar databases, will mismatch in many ways. 5 Examples: Incompatibilities Lexical : addr in one DB is address in another. Value mismatches : is a red car the same color in each DB? Is 20 degrees Fahrenheit or Centigrade? Semantic : are employees in each database the same? What about consultants? Retirees? Contractors? 6 What Do You Do About It? Grubby, handwritten translation at each interface. Some research on automatic inference of relationships. Wrapper (aka adapter) translates incoming queries and outgoing answers. 7 Integration Architectures 1. Federation : everybody talks directly to everyone else. 2. Warehouse : Sources are translated from their local schema to a global schema and copied to a central DB. 3. Mediator : Virtual warehouse --- turns a user query into a sequence of source queries. 8 Federations Wrapper Wrapper Wrapper Wrapper Wrapper Wrapper 9 Warehouse Diagram Warehouse Wrapper Wrapper Source 1 Source 2 10 A Mediator Result User query Mediator Wrapper Wrapper Query Query Query Query Result Result Result Result Source 1 Source 2 11 Two Mediation Approaches 1. Query-centric : Mediator processes queries into steps executed at sources. 2. View-centric : Sources are defined in terms of global relations; mediator finds all ways to build query from views. 12 Example Suppose Dell wants to buy a bus and a disk that share the same protocol. Global schema : Buses(manf,model,protocol) Disks(manf,model,protocol) Local schemas : each bus or disk manufacturer has a (model,protocol) relation --- manf is implied. 13 Example: Query-Centric Mediator might start by querying each bus manufacturer for model-protocol pairs....
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cs345-5 - 1 Information Integration Mediators...

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