DCIT 55 - Reviewer for ER Model and Database Concepts

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What is a primary key?

An attribute that uniquely identifies any given entity.

Define the SAVEPOINT command.

This command marks and saves the current point in the processing of a transaction.

Explain the purpose of a data dictionary.

It provides a detailed accounting of all tables found within the user/designer-created database.

What is the relational model?

It enables programmers to view data logically rather than physically. Signup and view all the answers

Describe Existence independence.

It is an entity that can exist apart from one or more related entities. Signup and view all the answers

What does ROLLBACK command do?

It terminates the current transaction and undoes any changes made during the transaction. Signup and view all the answers

Explain the concept of a Multivalued Attribute and provide an example.

A Multivalued Attribute is an attribute that can have many values. For example, in a student table, the 'hobbies' attribute can be multivalued, allowing a student to have multiple hobbies. Signup and view all the answers

What is a Secondary Key and how does it differ from a Candidate Key?

A Secondary Key is a key used strictly for data retrieval purposes. In contrast, a Candidate Key is a super key without redundancies and can be used to uniquely identify a row in a table. Signup and view all the answers

Explain the purpose and functionality of a COMMIT statement in database management.

A COMMIT statement is used to permanently save any transaction into the database. Once a transaction is committed, its changes become permanent and visible to other transactions. Signup and view all the answers

What is an ER diagram and what role does it play in database design?

An ER diagram is a graphical representation of a conceptual database viewed by an end-user. It forms the basis of an ER model and is used to visually depict the entities, attributes, and relationships in a database. Signup and view all the answers

Define a Derived/Computed attribute and provide an example in the context of a sales database.

A Derived/Computed attribute is an attribute whose value may be calculated from other attributes. For example, in a sales database, the 'total_sales' attribute of a salesperson can be a derived attribute calculated by summing the 'sales_amount' of individual transactions. Signup and view all the answers

Describe the characteristics and limitations of a single-user database.

A single-user database supports only one user at a time and is typically a desktop database running on a personal computer. Its main limitation is the inability to handle concurrent access or support multiple users simultaneously. Signup and view all the answers