nSimilar to types and
variables in programming languages
nSchema – the logical structure
of the database
He.g., the
database consists of information about a set of customers and accounts and the
relationship between them)
HAnalogous to
type information of a variable in a program
HPhysical schema: database design at the physical level
HLogical schema: database design at the logical level
nInstance – the actual content of
the database at a particular point in time
HAnalogous to
the value of a variable
nPhysical
Data Independence –
the ability to modify the physical schema without changing the logical schema
HApplications
depend on the logical schema
HIn general,
the interfaces between the various levels and components should be well defined
so that changes in some parts do not seriously influence others.
Data Models
nA collection of tools
for describing
Hdata
Hdata relationships
Hdata semantics
Hdata constraints
nEntity-Relationship
model
nRelational model
nOther models:
Hobject-oriented
model
Hsemi-structured data
models
HOlder models: network
model and hierarchical model
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