4. Relational Databases Flashcards
What is the definition of a database
A set of interrelated, centrally coordinated data files that are stored with as little data redundancy as possible.
What is the goal of a database
Efficiently and centrally coordinated information for a related group of files
A file is a related group of records
A record is a related group of fields
A field is a specific attribute of interest for the record
Distinguish between a database and a file based system
Database definition: a set of interrelated, centrally coordinated data files that are stored with as little data redundancy as possible.
Wheres a file based system are not connected across between sales, shipping and billing departments.
Describe schemas
A schema is a description of the data elements in a database, the relationships among them, and the logical model used to organize and describe the data.
What are the three levels of schema
External-level = individual user’s view
Conceptual-level = enterprise wide view of the entire database
Internal-level = low level view, how data are stored and accessed physical
What are the three Data Base Management Systems (DBMS) languages
Data definition language (DDL), Data Manipulation Language (DML) and Data Query Language (DQL)
Describe data definition language (DDL)
DDL builds the data dictionary,
creates the database
describes logical views for each user
specifies record or field security constraints
Describe the data manipulation language (DML)
DML changes database content, including data element creations, updates, insertions and deletions
Describe the data query language (DQL)
DQL enable users to retrieve, sort and display specific data from the database.
Describe what a relational database is, how it organizes data
The relational data model represents conceptual- and external-level schemas as if data are stored in two-dimensional tables.
What are the reason to have a set of related tables?
Data stored in one large table will be redundant and inefficient. Related Tables will help solve the following problems: Update anomaly, insert anomaly and delete anomaly
Relational Database – external level view individual user’s view
External-level view represents the conceptual and internal schema as if that “data view” were truly stored in one table.
Although the external-level view appears to the user that information is in one big table, it really is a set of tables that relate to one another.
