aChapter 15 - Overview The design process in multidatabase...

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Overview The design process in multidatabase systems is bottom-up. The individual databases actually exists Designing the global conceptual schema (GCS) involves integrating these local databases into a multidatabase. Database integration can occur in two steps: Schema Translation and Schema Integration . Database 1 Database 2 Database 3 Translator 1 Translator 2 Translator 3 InS 1 Intermediate schema in canonical representation InS 2 InS 3 INTEGRATOR GCS
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Network Data Model (Review) There are two basic data structures in the network model: records and sets . DEPARTMENT (DEPT-NAME, BUDGET, MANAGER) EMPLOYEE (E#, NAME, ADDRESS, TITLE, SALARY) Record type : a group of records of the same type. Set type : indicates a many-to-one relationship in the direction of the arrow. Representation of set instances: Employs owner record type set type member record type Database Jones, L. Patel, J. Vu, K. DEPARTMENT (owner record) STUDENT (member records)
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Example: Three Local Databases Database 1 (Relational Model): S (TITLE , SAL) E (ENO , ENAME, TITLE) J (JNO , JNAME, BUDGET, LOC, CNAME) G (ENO, JNO , RESP, DUR) Database 2 (Network Model): DEPARTMENT (DEPT_NAME, BUDGET, MANAGER) EMPLOYEE (E#, NAME, ADDRESS, TITLE, SALARY) Employs
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Example: Three Local Databases Database 3 (ER Model): Project No. Project Name Responsibility Engineer No. Engineer Name Title Salary Budget Location Duration Contract Date CONTRACTED BY CLIENT 1 Address Client Name ENGINEER WORKS IN N PROJECT 1 N
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Schema Translation: Relational to ER S (TITLE , SAL) E (ENO , ENAME, TITLE) J (JNO , JNAME, BUDGET, LOC, CNAME) G (ENO, JNO , RESP, DUR) ENO TITLE SAL E PAY S N M N 1 N M From our knowledge of the semantics of the database, we know E & J have a many-to-many relationship. JNO JNAME ENAME RESP J G CNAME DUR LOC BUDGET Treat salary as an attribute of an engineer entity JNO JNAME ENO ENAME RESP E J G TITLE SAL CNAME LOC BUDGET DUR Relationships may be identified from the foreign keys defined for each relation.
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Schema Translation: Network to ER WORK DEPARTMENT EMPLOYEE Map each record type in the network schema to an entity and each set type to a relationship. Network model uses dummy records in its representation of many-to-many relationships that need to be recognized during mapping. WORK Employs Works-in DEPARTMENT EMPLOYEE EMPLOYS WORKS-IN 1 1 N N DEPARTMENT EMPLOYEE EMPLOYS N M
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Schema Integration Schema integration follows the translation process and generates the GCS by integrating the intermediate schemas. Identify the components of a database which are related to one another. Two components can be related as equivalent, one contained in the other one, overlapped, or disjoint. Select the best representation for the GCS. Integrate the components of each intermediate schema.
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Integration Methodologies Integration Proces Binary: Decreases the potential integration complexity and lead toward automation techniques.
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