¡Is a column or set of columns that is a
primary key in another table
¡PROPERTIES
lvalue can be null,
lvalue can change
lvalue can be duplicated
¡RULES FO FK
lValue must refer to the existing
PK
DATABASE DEVELOPMENT
¡Database development is a process consisting
of many steps.
1.Data modeling.
2.Description of
the data to the db
3.Physical
implementation of the db
1. CUSTOMER REQUIREMENTS
¡Customer Questions:
lAsk specific questions during the interviews to help define the requirements.
li.e
who: who are the end users of he system?
lWho is requiring output form the system etc
lWhat: what is the primary purpose for this system?
lWhat does our end user want? Etc
lWhy: why do they need a db?
lHow do data in the system be inserted?
lWhere will the db system be maintained?
¡Customer agreement
lFrom your customer interviews,
you have documented and agreed upon a set of system requirements for
the new database.
l
lNow, the next step is to
translate these requirements into a db model.
2. ENTITIES
IDENTIFICATION
¡From customer requirements you can determine
entities and data attributes also you can determine the relationships btwn the
entities.
¡ENTITIES:
lAn entity defines a thing that
exists and distinguishable from which data will be collected. E.g person, place, object or concept
lEntities are basic building
blocks of the database design.
lEntity Instance: Is a particular occurrence of
an entity eg. Person etc
lEntity set: A group of similar entities is
called an entity class or entity type.
¡
Has laoreet percipitur ad. Vide interesset in mei, no his legimus verterem. Et nostrum imperdiet appellantur usu, mnesarchum referrentur id vim.
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