Week 1 Flashcards
what does DBMS mean
the software used to create and maintain data base systems
Are data and programs external to the DBMS
Yes they are external to the DBMS software as the DMS doesnt relate to the specific application
essentially all the relevant data isnt part of DBMS
what does meta data mean
The description of the data
What is a data model
concepts to describe the:
- structure of data
- the operations to manipulate these structures
- constraints
what is the database system
Both the DBMS software and the data itself
applications can also be included
Purpose of DBMS ( 4 things)
. defines a particular database in terms of its data types, structures and constraints
. create or load initial database onto a secondary storage medium
.Manipulating data:
- updating / removing data from a
database
- ACCESSING DATA THROUGH WEB APPS
- QUERYING , GENERATING REPORTS
. processing and sharing by multiple users and applicating programs WHILE ensuring all data is still valid and consistent
why is it important to define data types
To ensure only valid data types are in required fields keeping data consistent
advantages of DBMS
ADVANTAGES:
Controlling redundancy in data storage and in development and maintenance efforts.
* Providing multiple interfaces to different classes of users, facilitate sharing data across users.
* Restricting unauthorised access to data.
* Providing Storage Structures (e.g. indexes) for efficient
query processing (buffering/caching).
* Providing backup and recovery services.
* Representing complex relationships among data.
* Enforcing integrity constraints on the database.
* Drawing inferences and actions from the stored data using deductive and active rules
disadvantage of DBMS
Main inhibitors (costs) of using a DBMS:
o High initial investment and possible need for additional hardware.
o Overhead for providing generality, security, concurrency control,
recovery, and integrity functions.
* When a DBMS may be unnecessary:
o If the database and applications are simple, well defined, and not
expected to change.
o If there are stringent real-time requirements that may not be met
because of DBMS overhead.
o If access to data by multiple users is not required
what is a mini world
The real world domain that the database is designed for
What is an advantage of program data independence
.Caters for variety of (levels of) users
- user does not need to now specifics of the data to operate
. adapt to many different applications as programs and the data are independent
What is data abstraction ( characteristic of data approach)
. data storage details hidden and instead user is presented with a conceptual view of data base
. programs refer to data model constructs ( tables , records, objects, relationships) instead of storage details
multiple views (second characteristic of data approach)
each user can see a different view of data base where only data that is of interest to that user is described
What is redundancy
Having copies of the same data in different parts of a database
How can redundancy lead to problems
Every instance of that same data would have to be updated individually rather than just updating it once
When to not use a DBMS
.When it is too costly:
- ensuring concurrent access/ transactions , security … may be too costly
. when it isnt necessary:
- data is simple or well defined
- single ( or a very limited no of ) users required to access data
. When no DBMS will satisfy:
. real world constrainst like time constrainst that may not be met due to time penalty for using DBMS
. not able to handle complexity of data due to modelling limitations
. special operations required by user that DBMS doesnt support
what are data model operations
operations used for database updates or retrievals that refer to the constructs ( eg table , entities ,elements) rather than storage details
what is the difference between basic - model operations and user defined operations
basic model operations are those foundatianal , primitive operations ( Insert , update , delete , select) predefined and already provided by DBMS
whilst user defined are customised operations defined by user for their specific needs
give 4 examples of basic model operations
select, insert, update , delete
Database state
The data in the data base AT THAT PARTICULAR MOMENT IN TIME
what is database schema
The description of a database eg:
. headings of tables, the name of tables ,
.basically descriptions of database structure, data types and constraints on the database
Internal schema
descibes physical storage structures and access paths
conceptual schema
describes the structure and constraints of the full database for the whole community of users
- uses conceptual or implementational data model
external schema
describes a specific subset of the database for the desired group of users based on their interests ( and so supports multiple views
- same data model as conceptual schema
What does the data definition language (DDL do)
. used to specify conceptual schema
. In many DBMS used to define internal and external schema
What does the SDL ( storage definition language) do in some DBMS
. defines internal and external schema in some DBMS
What does DML (data manipulation language) do
it specifies the retrieval and update operations
How is DML expressed
Through general purpose programming languages like java, c , c++ …
OR
through standalone DML commands that are applied directly to database
What is a centralised DBMS
. combines DBMS , hardware , programs, user interface processing software into a single system
Can a user acces centralised DBMS remotely
Yes, but centralised DMMS does all the processes
Give three example of traditional data models
relational , hierachical , network
2 examples of emerging
object oriented , object relational
Homogenous DBMS
same DBMS in all sites
Heterogenous DBMS
Multiple autonomous DBMS connected via a network
