IT - Databases
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Individual, unrelated files.
Collection of related data.
Advantages of databases:
- Less redundancy
- Inconsistency avoidance
- Data integrity
Defines, creates and maintains a database.
DATABASE MANAGEMENT SYSTEMS (DBMS)
A DBMS is a combination of five components:
- Data Users
Two (2) categories of data users:
- End Users
- Application Programs
The American National Standards Institute/Standards Planning and Requirements Committee (ANSI/SPARC) has established three-level architecture for a DBMS:
- Internal level
- Conceptual level
- External level
Determines where data is actually stored on the storage devices.
Defines the logical view of the data.
Interacts directly with the user (end users or application programs).
> defines the logical design of data.
> also describes the relationships between different parts of the data.
3 database models used:
- Hierarchical database model
- Network database model
- Relational database model
Data is organized as an inverted tree. Each entity has only one parent but can have several children.
Hierarchical database model
At the top of the hierarchy, there is one entity, which is called the ____.
The entities are organized in a graph, in which some entities can be accessed through several paths.
Network database model
Data is organized in two-dimensional tables called relations. The tables or relations are, however, related to each other
Relational database model
2-dimensional tables are called ____.
The data is represented as a set of relations.
Relational Database Management System (RDBMS)
A relation in an RDBMS has the following FEATURES:
A name that is unique among other relations.
Each column in a relation is called an ______.
Each row in a relation is called a ____.
9 OPERATIONS ON RELATIONS
- Insert Operation
- Delete Operation
- Update Operation
- Select Operation
- Project Operation
- Join Operation
- Union Operation
- Intersection Operation
- Difference Operation
Instead of discussing these operations in the abstract, we describe each operation as defined in the database query language _____________.
SQL (Structured Query Language)
> is the language standardized by the American National Standards Institute (ANSI) and the International Organization for Standardization (ISO) for use on relational databases.
> it is a declarative rather than procedural language, which means that users declare what they want without having to write a step-by-step procedure.
Structured Query Language (SQL)
Uses several geometric shapes.
- Lines link
Represent entity sets.
Represent relationship sets.
Attributes to entity sets and link entity sets to relationships sets.
Is the process by which a given set of relations are transformed to a new set of relations with a more solid structure.
Two other common models:
- Distributed Databases
- Object-oriented Databases
Is not a new model, but is based on the relational model. However, the data is stored on several computers that communicate through the Internet or a private wide area network.
Tries to keep the advantages of the relational model and at the same time allows applications to access structured data.
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