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|---|---|---|---|---|
| 13-databases-1 |
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What is a database
- an integrated collection of data
- implicit properties
- represents some aspect of th real world, called miniworld
- is a coherent collection of data with inherent meaning
- is designed built and populated with data for a specific purpose
DBMS
- a software system designed to store, manage, and facilitate access to the database
- Oracle, SQL erver, MySQL, MonogDB
Application program
- a program that provides access to the dtabase by sending queries and requests for data to the DBMS
This course
- modelling and design of DBs
- programming (SQL + appliation development)
- DBMS implementation
specifiically relational databases
- ER modelling
- datbase normalisation
- SQL
relational vs nosql
relation is better for structured data, nosql is better for abstract data, as it is more flexible
Data modelling
first step in designing database
- create a data model for a specific problem domain
a model is Defn: a collection of concepts that can be used to describe the structure of a database such as data types, relationsips, and contraints that should hold for the data
schema Defn: a collection of metadata that describes the logical view of a database
noSQL databases are either schema-free or have relaxed schemas
conceptual data modelling
model the data close to the way the users percieve the data
ER model
- popular high level conceptual model
- uses diagrammatic notations - er diagram (ERD)
three notations
- chens notation
- crows foot notation
- UML notation
Example
how to model
entities
- a thing in the real world with independent existence
- physical existence
- conceptial existence
entity type is a collection of entities with the same attributes — represented by a rectangle
attribute
- a property of an entity
- simple (atomic) e.g, first name
- composite (can be divided) e.g., address
- single value e.g., id number
- multi value e.g., siblings
- stored - by default
- derived - drawn as dashed ovals e.g., age is derived from birth date
- key
- unique
- simple or composite
- underlined in ERD
relationships
a relationship model the connection between entitiy types
e.g., each employee works for one department
relationship type is a set of relationsihps among entities from the particular entity types - represented by diamonds
relationship types can have attributes
properties
- degree
- binary binary relationship|200
- n-ary n-ary relationship|300
- cardinality for binary relationships
- one to one
- one to n
- m to n
