Database
From Wikipedia, the free
encyclopedia
·
Database refers to information and its
supporting data structure- it is NOT the database management system
·
A database data collection with a management
system (DBMS) is called a database system- This implies that it is managed to
some level of quality
Examples of DBMS- Oracle, IBM DB2,
Microsoft Access, MySQL
·
Not generally portable but some can
inter-operate to support single app
·
Different classifications are contingent of the
content- Bibliographic, document-text, Statistical, Multimedia – Or App Area –
Accounting, Music Comp, Movies, Banking
·
Key objectives of first databases was efficiency,
to make data independent of logic of application programs
·
Two main data models were the hierarchical model
and the Codasyl model- followed by the Relational model
·
Notable research of databases- Relational &
Entity relationship models
Database Types
-Active
database
- Cloud
database
-Data
warehouse
-Distributed
Database
-Document-oriented
database
-Embedded
Database
-End-user
Database
-Federated
Database and Multi
Usage Requirements for Major Databases
-Functional
Requirements
-Defining
the structure of data
-Manipulating
the data
-Protecting
the data
-Describing
processes
-Operational
-Availability
-Performance
-Isolation
-Recovery
-Backup
-Data
independence
-
Languages are tailored to define a database,
manipulate its content, query it
-
Database design is done to meet needs of
end-users within a given app/info system
-
ERM is commonly used for design
-
Database storage is a container of the physical
materialization of a database
-
Data is encoded by assigning a bit pattern to
each language
Entity–relationship model
From Wikipedia, the free encyclopedia
-
Peter
Chen composed an article proposing techniques for ER in 1876
-
ER
= Relationship Model – a database
-
Relational
Database stores info in tables, sometimes leads to other tables
-
3
Schema Approach – conceptual data model (highest), Logical model (does not
require conceptual ER model), Physical model (contains enough detail to make a
database)
-
Entity
is capable of an independent existence- computers, employees, songs (examples)
-
Relationships
show how entities are related to one another, linking them together
-
Chen
uses marriage and the two roles of husband and wife to illustrate relationship
and its roles
-
A
semantic model is a model of concepts – platform independent model –
intensional model
-
Diagramming
Conventions- Chen uses rectangles to represent entities and diamonds represent
relationships for first class objects –attributes are ovals
-
ER
is limited because it is inadequate for systems that information cannot be
readily represented in relational form
PHLONX
3 Normal
Forms
- No repeating elements or groups of elements
- No partial dependencies on a concatenated key
- No dependencies on non-key attributes
- Normalization is the way the relationship
between data is perceived
- Normalization allows the user/creator to “ask”
the database specific questions
- Initially duplication is increased
- Objective of second normal form is for part
one not to depend on the concatenated key
- NF1 addresses atomicity and the need for
primary key
- Primary key uniquely identifies a row
- Concatenated primary key is when the value has
two or more columns
- The second normal form has been completed when
the orders have a single column primary key
Muddiest Point: Entity Relationship Model
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