Distributed Database Management Systems: Lecture 24. The main topics covered in this chapter include: fragmentation; design phase and have got the predicates to be used as basis for PHF; name our fragments/local tables as custQTA, custPESH;...
Distributed Database Management Systems Lecture 24 Distributed Database Management Systems Virtual University of Pakistan Fragmentation • We know there are different types, we start with the simplest one and that is the PHF • Supposedly, you have already gone through the design phase and have got the predicates to be used as basis for PHF, just as a reminder • From the user queries, we first collect the simple predicates and then we form a complete and minimal set of minterm predicates, a minterm predicate is … , you know that otherwise refer back to lecture 16, 17 • Lets say we go back to our Bank example, and lets say we have decided to place our servers at QTA and PESH so we have two servers where we are going to place our PHFs • As before we register our servers and now at our Enterprise Manager we can see two instances of SS • At each of the three sites we define one database named BANK and also one relation, normal base table, however, for the fragmentations to be disjoint (a correctness requirement) we place a check on each table at three sites, how… • We name our fragments/local tables as custQTA, custPESH • Each table is defined as create table custPESH(custId char(6), custName varchar(25), custBal number(10,2), custArea char(5)) • In the same way we create tables one at each of our two sites, meant for containing the local users • Users that fall in that area and the value of the attribute custArea is going to be the area where a customer’s branch is, so its domain is {pesh, qta) • To ensure the disjointness and also to ensure the proper functioning of the system, we apply a check on the tables • The check is • Peshawar customers are allocated from the range C00001 to C50000, likewise • Create view custG as select * from custPesh Union All select * from QTA.bank.dbo.custQTA • Likewise, we have to apply same command at QTA • Create view custG as select * from custQta Union All select * from PESH.bank.dbo.custPesh • Once it is defined, now when you access data from custG, it gives you data from all four site • It is also transparent • Now lets say if you are connected with Pesh, and you give the command Select * from custPesh You get the output • Same is the case with the users of the QTA server, they pose the query • Select * from custQTA • Like a local user • The previous two examples represent access of a local user, now if the global users, like from Management, want to access data across all sites, they will pose the query against the global view, like • Select * from custG • All this is transparent from the user, that is, the distribution of data • Global user gets the feeling, as if all the users’ data is placed on a single place • For the administrative purposes they can perform analytical types of queries on this global view, like Thanks .. .Distributed Database Management Systems Virtual University of Pakistan Fragmentation • We know there are different... minimal set of minterm predicates, a minterm predicate is … , you know that otherwise refer back to lecture 16, 17 • Lets say we go back to our Bank example, and lets say we have decided to place... our Enterprise Manager we can see two instances of SS • At each of the three sites we define one database named BANK and also one relation, normal base table, however, for the fragmentations to