Database Systems vs. Files and DBMS Characteristics

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What is a DQL?

- DQL = used to INTERROGATE the database - Retrieves, sorts, orders, presents subsets of the database in response to user queries - Example is SQL

What is a DML?

-DML = Data manipulation language -Update, insert, delete portions of the database -Usually a verb

What are the two components of a DBMS?

1. Data Dictionary 2. DBMS Languages

Define DBMS

-Program that MANAGES and CONTROLS ACCESS to the database -Defines data structures for an IT application -DBMS controls the database so that users can access, query, or update it without reference to how or where the data are physically stored

What is a DBMS language used for?

-The sets of commands used to do three things: CREATE, CHANGE, and QUERY the database -Types of DBMS languages are called data definition language, data manipulation language, and data query language

What is a tuple?

Each row in a relation

What are the three levels of schemas?

1. Conceptual level schema 2. External level schema 3. Internal level schema

What are the problems with file-based approaches?

1. Duplication of data 2. Specific data values stored in different files are not consistent

What is a Data Dictionary?

A read-only set of tables that provides information about the database, containing: - definitions of schema objects - rights of access for each user - information about who has accessed or updated schema objects - how much space allocated for schema objects - names of users

How is the logical and physical view of data different?

AKA "Program-data independence" -Logical = how programmer conceptualizes data -Physical = how it is physically arranged and stored on disk, tape, CD, or other media

Define conceptual-level schema

An organization-wide view of the entire database

Define a database system

Combination of 1. the database 2. the DBMS 3. and application program that uses the database

Define external-level schema

Consists of a set of individual user views of PORTIONS of the database (also called a subschema)

What are advantages to the database approach?

Controlled data redundancy, consistent data, integrated data, shared data, eases application development

What is a DDL?

DDL = Data definition language Used to build the data dictionary and create the database

Define an internal-level schema

Provides a low-level view of the database

What is a schema?

Schema describes logical structure of a d.b.

SQL

Structured Query Language -a standard query language for requesting information from a database (DQL)


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