Block 2, Part 3: The Database Context Flashcards
What is an information system?
A collection of hardware, software and processes that enables organisations to manage and process data and to produce information.
What constitutes the processing of data?
Any activity involved in collecting, filtering, integrating and exploring the data.
What is a replicated database?
A single database whose contents are replicated to multiple server sites, allowing ‘local’ access requests to a copy of the data.
What is a federated database?
A collection of DBMSs on multiple servers that collectively manage data content.
What is a relational database?
A DBMS built on the relational model of data, typically using SQL for data definition, control and access.
What is a non-relational database?
A DBMS using non-relational models of data - hierarchical, object-oriented, etc.
What is the domain of discourse?
The collection of data that is significant to an organisation.
What is meant by ‘persistent data’?
Data is held in long-term storage and endures beyond the execution time of the software that manages and accesses it.
What is meant by ‘shared data’?
Data is available to multiple processes.
What is meant by ‘interrelated data’?
Individual data elements held in the database can be managed and processes as collections.
What is a database management system?
Any software system that manages one or more databases.
What is a schema?
A data definition that describes a data collection.
What is a logical schema?
A schema which defines the logical properties of data in a database - the representation and associated constraints.
How many logical schemas does a database have?
Just one.
What does a logical schema comprise in a relational database?
The relational tables, the logical links between them (foreign keys), and any constraints on the data values.
What is a storage schema?
A schema that defines how a database is stored in files and accessed, which must relate to the definitions in a logical schema (via a mapping).
How many storage schemas does a database have?
Just one.
What is an external schema?
A schema which defines data accessible through the DBMS for a specifies group of user processes, which must relate to the definitions in a logical schema (via a mapping).
How many external schemas does a database have?
There can be several external schemas, depending on the differing needs of the users and applications.
When does logical data independence exist?
When a change to a logical schema has no impact on application code.
When does physical data independence exist?
When a change to the storage schema has no impact on the applications.
