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I am interested to apply for a job position in your company.Iam a Kenyan citize
Database Fundamentals: 15File: N_drive:\jhu\class\1995\db-fund.ppt
1994, 1995 Robert Robbins
Relations as a Database
Codd recognized that many of the files used in computerized
information systems were very similar in structured to tabularized
Physical System Database
Database Fundamentals: 7File: N_drive:\jhu\class\1995\db-fund.ppt
1994, 1995 Robert Robbins
Relational Database Model
What is a relational database?
a database that treats all of
A database is a persistent, logically coherent collection of inherently
meaningful data, relevant to some aspects of the real world.
The portion of the real world relevant to the database is sometimes
referred to as the universe of discourse or as the da
Davies, Recovery Semantics for a DB/DC System," Proceedings ACM
National Conference, 1973, pp. 136-141. (The above two companion
papers are the seminal work in the field. Anyone interested in the topic
of software recovery should read them both at least t
5.8.7. HISTORICAL NOTE ON RECOVERY MANAGEMENT.
Most of my understanding of the topic of recovery derives from the
experience of the IMS developers and from the development of System
Unfortunately, both these groups have been more interested in
Recovery management consists of two components.
o Recovery manager that is responsible for tracking transactions and the
coordination of transaction COMMIT and ABORT, and system
CHECKPOINT and RESTART (see below).
o Log manager that is used by recovery ma
DICHOTOMIZE WINNERS AND
REDO THE WINNERS;
END RESTART; It is important that the REDOs occur
before the UNDO (Do you see why (we are assuming page-locking and
high-water marks from log-sequence numbers?)
As it s
transaction commits (successfully completes), the effects of the
transaction cannot be blindly undone. Rather, to undo a committed
transaction, one must resort to compensation - running a new transaction
that corrects the errors of its predecessor. Compen
If a transaction does work at several nodes of a network then it will
require a process structure (cohort) to represent its work at each
participating node. Such a transaction is called distributed.
The following table summarizes the possibilities and
IF FAIL THEN
PERFORM PHASE 2 COMMIT;
INFORM LAST THAT COMMIT
following gives a picture of a three deep nest:
o Performance monitor: Keeps statistics about system performance and
o Lock component: maintains the locks (synchronization primitives).
o Recovery manager: implements the notion of transaction COMMIT,
ABORT, and handles system restart.
o Log manag
S = < 2,4 >
C = < Marshall, Eisenhower, Bradley >
A set may consist of an unordered collection of ordered tuples. For
example, we could imagine the set of all ordered pairs of integers, such
that the first element is the square root of the second element.
o BACKUP_TRANSACTION: undoes the effects of a transaction to an
earlier save point.
o COMMIT_TRANSACTION: signals successful completion of
transaction and causes outputs to be committed.
o ABORT_TRANSACTION: causes undo of a transaction to its initial
18.104.22.168. LOG ARCHIVE AND CHANGE ACCUMULATION
When the log is archived, it can be compressed so that it is convenient
for media recovery. For disk objects, log records can be sorted by
cylinder, then track then sector then time. Probably, all the records
Note: Cartesian products may be generated by multiplying any number
of sets together. The actual number of sets involved in a particular case
is said to be the degree or arity of that Cartesian product.
Note: Relations may be of any degree (arity).
maintain data integrity
provide for backup and recovery
allow data independence
provide non-procedural query language
perform automatic query optimization
Database Fundamentals: 5File: N_drive:\jhu\class\1995\db-fund.ppt
Fruits have for so many years been used for various medicinal and health benefits. This can be
attributed to the fact that most fruits contain zero calories unlike other foods which are known to
tremendously help one add weight. Other reasons c
GENERAL COMPETENCY DETAILS/REQUIREMENTS
Seeing the big picture Level 4
Seeing the big picture is about having an in-depth understanding and knowledge of how your role fits
with and supports organizational objectives and the wider public needs, it is about
Vision and other special senses
Pigs have colour vision and a panoramic range of about 310, and binocular vision of 3550. It
is thought they have no accommodation (i.e., they cannot focus). Pigs are inquisitive and this
must be remembered when moving
Animal Welfare: What Is It?
Animal welfare means how an animal is coping with the conditions in which it lives. An animal
is in a good state of welfare if (as indicated by scientific evidence) it is healthy, comfortable, well
nourished, safe, able to expr
KESSES SUB COUNTY
Action plan from previous meetingwhat has been done
Proposed Action from
last quarters Action plan
Number of Sub
Counties in the
Number of sub
111-11-1111 Ziegler Samual 7272 Cherry Ln. Baltimore MD 21208 L.
Database Fundamentals: 19File: N_drive:\jhu\class\1995\db-fund.ppt
1994, 1995 Robert Robbins
Yet another re
to be a foreign key. Columns containing foreign keys are subject to an
integrity constraint: any value present as a foreign key must also be
present as a primary key.
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10 MAY 44
31 MAR 59
7 AUG 90
1 DEC 66
11 APR 60
An essential attribute of a relation is that every tuple must be
and should never be changed. Sometimes none of the candidate keys for
a relation are likely to remain stable over time. Then, an arbitrary
identifier might be created to serve as a primary key. Such arbitrary
keys are also known as surrogate keys.
Starting two sets.
A Cartesian product of two sets can be generated by combining every
member of one set with every member of the other set. This results in a
complete set of ordered pairs, consisting of every possible
A relation, therefore, must always be representable as a subset of some
A Cartesian product pairs every member of the first set with every
member of the second set.
A relation pairs some members of the first set with some members
22.214.171.124. SUMMARY OF RECOVERY PROTOCOLS
inconsistencies due to concurrency.
o The DO-REDO-UNDO log record protocol allows for and
o The write-ahead-log protocol insures that th