11-04-2012, 04:54 PM
Database Management Systems
computer seminar.ppt (Size: 152 KB / Downloads: 112)
What kind of data ?
Enterprise data
Banking
Supermarkets, Sales
Airlines
Universities
Manufacturing
Human resources
More recent:
Semi-structured Data (XML)
Scientific data
Biological data
Sensor network data etc etc…
DBMS
Database Management Systems provide
Data abstraction
Key in evolving systems
Probably the most important purpose of a DBMS
Goal: Hiding low-level details from the users of the system
Guarantees about data integrity
In presence of concurrent access, failures…
Speed !!
Data Modeling
A data model is a collection of concepts for describing data properties and domain knowledge:
Data relationships
Data semantics
Data constraints
We discussed two models:
Entity-relationship Model
Diagrammatic representation
Easier to work with
Syntax not important, but remember the “meaning”
Remember what you can model
Relational Model
Only one abstract concept
Closer to the physical representation on disk
Normalization
Data Integrity
Manage concurrency and crashes
Transaction: A sequence of database actions enclosed within special tags
Properties:
Atomicity: Entire transaction or nothing
Consistency: Transaction, executed completely, take database from one consistent state to another
Isolation: Concurrent transactions appear to run in isolation
Durability: Effects of committed transactions are not lost
Consistency: Transaction programmer needs to guarantee that
DBMS can do a few things, e.g., enforce constraints on the data
Rest: DBMS guarantees
Haven’t covered in class yet