IT 244 Database Management System. Lecture 1 – 14 / 02 /07 Course Information & Introduction to Database & DBMS. Topic 1 – Introduction. Evolution of Database Systems: Data >> Database vs Database Management Compare ways DATA is organized: Word processor (document production)
Lecture 1 – 14 / 02 /07
Introduction to Database & DBMS
File Information Stored
Patients - Surname, First name, age, date admitted, date discharged
Doctor - Surname, First name, Phone contact
Ward - Ward number, number of rooms
Room - Room number, beds, ward number
Since data is stored in many related files you can end up with:
A collection of data that is managed and organized by a DBMS. Not all collection of data are databases. Databases have the following characteristics:
Data are all in one database but kept in a separate logical units or tables.
The DBMS provides users with one interface to access the database and
present the database information to each users according to preferences.
In other words:
A collection of programs that enables you to store, modify, and extract information from a database. (Webopedia Computer Dictionary)
- DBMS goes far beyond the file system in providing flexibility, such as data structures that support efficient access to very large amounts of data
- Again the advantage of a DBMS over a file system is the flexibility to manipulate stored data in much more complex ways than the reading and writing of files.
In this type of System, the item of data include:-
- Reservations by customers
- Include names and addresses of customers, accounts, loans etc.
- as with airlines reservation system, we expect many tellers and staff or customers querying and modifying the bank’s data at once
i) isolation: - the appearance that transactions execute one at a time
ii) atomicity:- the requirement that transactions either completely or not at all
iii) durability:- the ability to recover from failure or errors of many types
- Data was composed of many small items
- Many queries or modifications were made
- Columns are headed by attributes which describe the entries in the column
Eg. A relation named Accounts recording Bank Account, Balance and Type might look like:
- Account No
SELECT account No
WHERE accountNo = 456
1. Examine all the tuples of the Relation Accounts mentioned in the FROM clause
2. Pick out those tuples that satisfy some criterion indicated in the WHERE clause and
3. Produce as an answer certain attributes of those tuples as indicated in the SELECT clause
In practice, the system must “optimize” the query and find an efficient way to answer the query, even though the relations involved in the query may be very large.
eg. Database of modest size are today stored on arrays of disks which are called secondary storage device. (compared to main memory which is primary storage)
- Tertiary Storage:-
- tertiary storage devices perhaps storing a tera-byte each.
- require much more time to access a given item than does a disk
- involve transporting an object, upon which the desired data item is stored to a reading device
- Parallel Computing
- the ability to store enormous volumes of data is important but it would be of little use if we could not access large amounts of data quickly
- thus very large databases also require speed enhancers.
- parallel Computing handle such problem