(Week 6) Databases Flashcards
What is data?
Data are bare facts with some meaning and recorded in some format
What is information?
Information is processed data that is in the form useful for making decisions
What are file-based systems?
A collection of application programs that
perform services for the end-users, such as the production of reports. Each program defines and manages its own data.
When is a file base system most suitable?
-fixed data,
-limited storage devices e.g.,
-embedded systems, single-user applications (no concurrent -accessneeded),
-where DBMS overhead is too high/expensive,
-less security constraints
What are the limitations of file base system?
-separation and isolation of data,
-duplication of data,
-data dependence,
-incompatible file formats,
-fixed queries/proliferation of application programs
What is a database?
“A shared collection of logically related
data and its description, designed to meet the information needs of an organization
What is a database management system/ database manager with an example?
A program that lets one or more computer users create and access data in a
database. E.g. MS SQL Server, Oracle, MySQL, SQLite, PostgreSQL, MongoDB
What is a Database catalogue/ data dictionary /meta-data with an example?
It’s data about data and provides details about database structure and constraints
e.g., type, length, storage
format and constraints on the data, date of creation
What is a data model?
An abstract representation of data entities, their properties, and rule explaining how these entities are associated with each other. Data modeling techniques:
i) Entity relationship diagrams; ii) Unified modeling language
What is an Entity?
An entity is a distinct object (a person, place, thing, concept or event)
What is an attribute?
A property that describes some aspect of an object that we wish to record
What are relationships?
An association between entities.
What are data administrators responsible for?
Responsible for data resources – planning,
procedures, design, maintenance of standards, policies etc.
What are database administrators responsible for?
Responsible for the physical realization of
the database – db design, implementation, security, integrity,
maintenance, performance, backup etc
What are database designers responsible for?
Responsible with identifying the data entities, relations,
constraints (business rules)
What are application developer responsible for?
Develop applications for end users. These
applications use data from one or more databases
What are end users?
They are the clients of the database
What are the advantages of DBMS?
Sharing of Data - Files owned by a single user – DB is owned by organizations
Control of Redundancy - Different users may have the same data (Names of students) – DB contains only one
occurrence of the same data
Data Consistency - Effect of eliminating redundancy. Data needs to be updated only once in one place.
Files are distributed and data needs to be updated in all of the files.
Improved Data Standards - DB Administrator (DBA) defines organization-wide standards on how to represent data
in a database. (format, conventions)
Better Data Security - Files are not secure. DB can give security to the very basic level.
Improved data Integrity - integrity constraints e.g., Only WDaDb students can get web development progress
reviews signed-off and work on Website Project
Faster Development of New Applications - A well-designed DB is always modular and helps in developing new
applications as most of the data can be retrieved by using queries
Better Data Accessibility - Query Language support allows any user to get data required anytime.
More Control of Concurrency - Simultaneous access by two or more users is allowed.
Better Backup and Recovery Procedures - Simple backup. Imagine backing up all the files of all the departments.
Support of different types of operations on data - CRUD – create, read, update, delete
ACID: Atomicity – transactions are all or nothing; consistency – valid
consistent data is saved; isolation – transactions do not affect each other;
durability – written data will not be lost.
Views: a subset of the database visible to users (e.g., a level of security,
customized appearance of database can present a consistent, unchanging
picture of the structure of database despite underlying changes to schema)
What is Data Definition Language?
Allows users to specify data types and structures and constraints
on the data to be stored in the database
o Examples: CREATE, ALTER, DROP, RENAME
What is Data Manipulation Language (DML)?
Allows users to insert, update, delete and retrieve data from the database Eg Query language – general inquiry facility and the most common one is Structured Query Language (SQL)
