Physical schema,logical schema and sub schemas
combines everything into a single system including, DBMS software,hardware, application programs and user interface
overall design of the database
A Database has three views. The External Schema: What the end user sees. The Internal Schema: What the programmers of the program see. The Conceptual Schema: The basic plan of the database. Most of the time this is in paper form as a Conceptual Schema Diagram (CSD)
The schema is the physical arrangement of the data as it appears in the DBMS. The subschema is the logical view of the data as it appears to the application program.
The schema is the physical arrangement of the data as it appears in the DBMS. The sub-schema is the logical view of the data as it appears to the application program.
a representation of DBMS design. It helps to design, develop, implement, and maintain the database management system. A DBMS architecture allows dividing the database system into individual components that can be independently modified, changed, replaced, and
SCHEMA is the physical arrangement of the data as it appears in the DBMS. SUB-SCHEMA is the logical view of the data as it appears to the application program.
the architecture of dbms contains three levels 1/ external level:different users views of the database,shows relevant data for a particular user. 2/conceptual level:global view pf the database;describes what data is stored and its relationships. 3/internal level:physical representation of the database on the computer, Describes how the data is stored in the database.
the overall logical data base description is referred to as a schema. it is sometimes also referred to as an overall modal of the data, a conceptual modal of the data, a conceptual schema
In 3 tier architecture, client directly interacts with intermediate server and intermediate server will directly interact with database server.
The distinction between database schema and database state is very important. When we define a new database, we specify its database schema only to the DBMS. At this point, the corresponding database state is the empty state with no data. We get the initial state of the database when the database is first populated or loaded with the initial data. From then on, every time an update operation is applied to the database, we get another database state. At any point in time, the database has a current state. The DBMS is partly responsible for ensuring that every state of the database is a valid state-that is, a state that satisfies the structure and constraints specified in the schema. The DBMS stores the descriptions of the schema constructs and constraints-also called the meta-data-in the DBMS catalog so that DBMS software can refer to the schema whenever it needs to. The schema is sometimes called the intension, and a database state an extension of the schema.
A reference architecture consists of:Set of global external schemas.Global conceptual schema (GCS).Fragmentation schema and allocation schema.Set of schemas for each local DBMS conforming to 3-level ANSI/SPARC .Some levels may be missing, depending on levels of transparency supported.Can be homogeneous or heterogeneous.Gaurav SinghG.N.I.T MCA,GREATER NOIDAContact: 9458660007