An Introduction to Database Systems 8Ed - C J Date - Solutions Manual Episode 2 Part 6 pot

Copyright (c) 2003 C. J. Date page 21.6

individual client, it looks like a regular DBMS.* However, the

data is stored, mostly, not at the middleware site, but rather at

any number of other sites behind the scenes, under the control of

a variety of other DBMSs (or even file managers). In other words,

the middleware product uses the combination of those other DBMSs

and/or file managers as its own storage manager (and coordinates

their operation, of course).

──────────

* In the case of DataJoiner, at least, it is a DBMS (among other

things). Why would you buy DB2 when you can buy DataJoiner

instead? (The question is hypothetical, or rhetorical, but the

point is that not all technical questions have technical answers!

The answer to this particular question probably has more to do

with IBM's marketing and pricing strategies than it does with

technical issues.)

──────────

21.7 SQL Facilities

Explain client/server capabilities──CONNECT, DISCONNECT, SET

CONNECTION (not in too much detail). By the way, note the syntax:

CONNECT TO but not DISCONNECT FROM (this point isn't mentioned in

the book). You could elaborate on SQL/PSM's stored procedure

support if you like, but it's complicated (see reference [4.20]).

Answers to Exercises

21.1 Location independence means users can behave (at least from a

logical standpoint) as if the data were all stored at their own

local site. Fragmentation independence means users can behave (at

least from a logical standpoint) as if the data weren't

fragmented. Replication independence means users can behave (at

least from a logical standpoint) as if the data weren't

replicated.

21.2 Here are some of the reasons:

• Ease of data fragmentation

• Ease of data reconstruction

• Set-level operations

• Optimizability

Copyright (c) 2003 C. J. Date page 21.7

21.3 See Section 21.2.

21.4 See Section 21.4.

21.5 See Section 21.4.

21.6 No answer provided.

21.7 No answer provided.

21.8 No answer provided.

*** End of Chapter 21 ***