Index
• Fundamentals of Database Systems.
• Three-Schema Architecture & Data Independence
• DBMS Languages, Interfaces & Classification
• Database System Environment
Fundamentals of Database Systems.
A data model is a collection of concepts used to describe the structure of a database like
specifying the data types, constraints etc.. MOst data models include a set of basic
operations to manipulate the data in the database. Like retrieval of data from the database
or updates on the data.. THe first category of data models is the high-level or conceptual
data model, then we have the representational or implementation data models and finally
low level or physical data models.. Database schema database schema is a description of a
database and metadata is a subset of metadata or it is one of the components of metadata.
THe data in the database at a particular moment in time is called as a database state or an
instance or snapshot. Each object. Within the database is called a schema construct like for
example the tables in database student course etc. These are called as schemas construct..
Three-Schema Architecture & Data Independence
The goal of this three schemas architecture is to separate the user applications and the
physical database.. schemas can be defined at three levels. The first level is the internal
level. This internal level has an internal schemas. the next level in our three schema
architecture is the conceptual level. each external schemas describes the part of the
database that a user is interested in and hides the other database from the user group..
data independence can be defined as the capacity to change the schemas at one level of a
database system without having to. change the schema at one. level. without data
independence. If we make any changes at the internal level or to the internal. schemas,
then we have to change higher levels too but with data. independence when we change the
schema at. one level, it does n't affect the schemas at higher levels. Schemas do n't change
frequently, but if required to change with this concept of data independence, any changes
will not affect the higher levels. called as mapping..
DBMS Languages, Interfaces & Classification
There is no clear separation between the conceptual and the internal schemas. for each
database users. We have different interfaces and languages provided by the DbMs for each
of these users.. This is all about the languages provided by DbMs that is the data definition
language and storage definition language. the programming language that is embedded in
the programming language is called the data sub language and a high-level DMl is also called
set at a time DMl because it can retrieve many records in a single DMl statement itself. the
formbased interfaces are designed and programmed for the nave users or parametric
users.. There are several criteria used to classify database management systems, so the
criterias could be based on data. model number of users, cost of DbMs, number of sites,
types of access path, generality and so on. We will briefly look into few of these criteria. the
