Some different database system architectures. (a) Shared nothing architecture.

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1 Figure.1 Some different database system architectures. (a) Shared nothing architecture. Computer System 1 Computer System CPU DB CPU DB MEMORY MEMORY Switch Computer System n CPU DB MEMORY

2 Figure.1 continued. (b) A networked architecture with a centralized database at one of the sites. Site (San Francisco) Central DB1 Site (Chicago) DB Site (New York) Site (Los Angeles) Communications Network Site (Atlanta)

3 Figure.1 continued. (c) A truly distributed database architecture. Site Site Site L Communications Network Site 3 Site (c) A distributed database on a network

4 Figure. Data distribution and replication among distributed databases EMPLOYEES San Francisco and Los Angeles PROJECTS San Francisco WORKS_ON San Francisco Employees San Francisco EMPLOYEES All PROJECTS All WORKS_ON All Chicago (headquarters) New York EMPLOYEES New York PROJECTS All WORKS_ON New York Employees Communications Network Los Angeles EMPLOYEES Los Angeles PROJECTS San Francisco and Los Angeles WORKS_ON Los Angeles Employees Atlanta EMPLOYEES Atlanta PROJECTS Atlanta WORKS_ON Atlanta Employees

5 Figure.3 Allocation of fragments to sites. (a) Relation fragments at site corresponding to department. (b) Relation fragments at site 3 corresponding to department. (a) EMPD FNAME MINIT LNAME SSN SALARY SUPERSSN DNO John Franklin Ramesh Joyce B T K A Smith Wong Narayan English DEP DNAME DNUMBER MGRSSN MGRSTARTDATE DEP_LOCS DNUMBER LOCATION Research - MAY-78 Bellaire Sugarland Houston WORKS_ON PROJS Data at Site PNAME Product X Product Y Product Z PNUMBER 1 3 PLOCATION Bellaire Sugarland Houston DNUM (b) EMPD FNAME MINIT LNAME SSN SALARY SUPERSSN DNO Alicia Jennifer Ahmad J S V Zelaya Wallace Jabbar DEP DNAME DNUMBER MGRSSN MGRSTARTDATE DEP_LOCS DNUMBER LOCATION Administration JAN-8 Stafford WORKS_ON PROJS Data at Site 3 PNAME Computerization Newbenefits PNUMBER PLOCATION Stafford Stafford DNUM

6 Figure. Complete and disjoint fragments of the WORKS_ON relation. (a) Fragments of WORKS_ON for employees working in department (C=[ IN (SELECT SSN FROM EMPLOYEE WHERE DNO=)]). (b) Fragments of WORKS_ON for employees working in department (C=[ IN (SELECT SSN FROM EMPLOYEE WHERE DNO=)]). (c) Fragments of WORKS_ON for employees working in department 1 (C=[ IN (SELECT SSN FROM EMPLOYEE WHERE DNO=1)]). (a) G1 G G C=C AND ( IN (SELECT PNUMBER WHERE DNUM=)) 0 C3=C AND ( IN (SELECT PNUMBER WHERE DNUM=1)) C1=C AND ( IN (SELECT PNUMBER WHERE DNUM=)) Employees in Department (b) G G G6 C=C AND ( IN (SELECT PNUMBER WHERE DNUM=)) C6=C AND ( IN (SELECT PNUMBER WHERE DNUM=1)) C=C AND ( IN (SELECT PNUMBER WHERE DNUM=)) Employees in Department (c) G7 G8 G9 C7=C AND ( IN (SELECT PNUMBER WHERE DNUM=)) C8=C AND ( IN (SELECT PNUMBER WHERE DNUM=)) null C9=C AND ( IN (SELECT PNUMBER WHERE DNUM=1)) Employees in Department 1

7 Figure. The five-level architecture in a federated database system (FDBS). Source: Adapted from Sheth and Larson, Federated Database Systems for Managing Distributed Heterogeneous Autonomous Data-bases. ACM Computing Surveys (Vol. : No. 3, September 1990). External External External Federated Federated Export Export Export Component Component Local Local Component DBS Component DBS

8 Figure.6 Example to illustrate volume of data transferred. SITE 1: EMPLOYEE FNAME MINIT LNAME SSN BDATE ADDRESS SEX SALARY SUPERSSN DNO 10,000 records each record is 100 bytes long SSN field is 9 bytes long FNAME field is 1 bytes long DNO field is bytes long LNAME field is 1 bytes long SITE : DEPARTMENT DNAME DNUMBER MGRSSN MGRSTARTDATE 100 records each record is 3 bytes long DNUMBER field is bytes long DNAME field is 10 bytes long MGRSSN field is 9 bytes long

9 (a) (b) EMPD attribute list: FNAME,MINIT,LNAME,SSN,SALARY,SUPERSSN, DNO guard condition: DNO= DEP attribute list: (all attributes DNAME,DNUMBER,MGRSSN,MGRSTARTDATE) guard condition: * DNUMBER= DEP_LOCS attribute list: (all attributes DNUMBER,LOCATION) guard condition: * DNUMBER= PROJS attribute list: (all attributes PNAME,PNUMBER,PLOCATION,DNUM) guard condition: * DNUM= WORKS_ON attribute list: (all attributes,,) guard condition: * IN (π SSN (EMPD)) OR IN (π PNUMBER (PROJS)) EMPD attribute list: FNAME,MINIT,LNAME,SSN,SALARY,SUPERSSN, DNO guard condition: DNO= DEP attribute list: (all attributes DNAME,DNUMBER,MGRSSN,MGRSTARTDATE) guard condition: * DNUMBER= DEP_LOCS attribute list: (all attributes DNUMBER,LOCATION) guard condition: * DNUMBER= PROJS attribute list: (all attributes PNAME,PNUMBER,PLOCATION,DNUM) guard condition: * DNUM= WORKS_ON attribute list: (all attributes,,) guard condition: * IN (π SSN (EMPD)) OR IN (π PNUMBER (PROJS)) Figure.7 Guard conditions and attributes lists for fragments. (a) Site fragments. (b) Site 3 fragments.

10 Database server Database server Database link CONNECT TO... IDENTIFY BY... DEPT Table EMP table Application TRANSACTION TRANSACTION Net8 Net8 Network HQ Database INSERT INTO DELETE FROM DEPT..; SELECT... FROM COMMIT; INSERT INTO DELETE FROM DEPT..; SELECT... FROM COMMIT;.. Sales database Figure.8 Oracle distributed database systems. Source: From Oracle (1997a). Copyright Oracle Corporation All rights reserved.