Oracle Database
Client failure (PMDS)
-Records are locked by any client performing insertions, deletions, or updates. -Locked records are not available to the other clients. -The locked records stay locked in the event of a client failure. -The transactions in progress at the time of failure are loss. - All users have to log off during the repair. -Data can be restored from the last backup, but the transactions since the last backup are lost and have to be reentered
Server Failure (Client/Server)
A central transaction log keeps a log of all current database changes
Client (PMDS)
Adds, deletes, and updates data
Server (Client/Server Databases)
Adds, deletes, updates, and filters data
Structured Query Language
Fourth generation, high-level, nonprocedural language
Client/Server Databases
Multiuser environment - runs the DBMS as a process on the server and runs a client database application on each client
Client Failure (Client/Server)
Only the fail client's transactions in progress are lost
Network Environment (Client/Server)
The client does not store any database. The server sends only requested data to client and less network traffic.
total dependency
a nonkey column is dependent on all primary key columns
transitive dependency
a nonkey column is dependent on another nonkey column
partial dependency
a nonkey column is dependent on part of the primary key
normalization
analyze tables
Optimistic table locking (PMDS)
assumes that no two transactions will happen at the same time on one table
associative entity
decomposition involves a third party; also known as a composite entity
EF Codd
developed relational databases
Higher normal form
lower redundancy
Decomposition
many-to-many relationships are allowed, but they are not easy to implement
third normal form
no transitive dependency
Database Management System (DBMS)
performs the required processing
Relational algebra
procedural language; uses a set of operations on tables to produce new resulting tables
Personal Database Management Systems (PDMS)
stored on a user's desktop computer or client computer
Network environment (PMDS)
system response depends on the speed of the network and amount of traffic
first normal form
table contains no multivalued columns
second normal form
there is no partial dependency. A nonkey column that is dependent on part of a composite key. Exists only in a table with a composite key
Purpose of Relational Database
to overcome the problem of 3rd generation high level language. Only 1 row of a table could be manipulated; Benefit: eliminated the need for a looping structure
Automatic table locking
two agents may not sell the same seat at the same time
