select sys_context( 'userenv', 'current_schema' ) from dual;
tablespace,segment,extent,oracle blocks.. are the logical schema of a database
A user in Oracle corresponds to a schema. Objects, such as table and indexes, must exist within a schema. Without creating a user/schema, use of the database will be limited to the built-in schemas and objects, such as the one-row DUAL table and standard PL/SQL packages.
the schema can be termed either conceptual or logical or physical. But mostly speaking, the term schema is used to refer to a logical structure.
Well, darling, in Oracle, a user is an account used to log in and access the database, while a schema is a collection of database objects (tables, views, etc.) associated with a particular user. So, think of a user as the key to the front door, and a schema as the fancy furniture and decor inside the house. You can have multiple schemas in a single user account, just like you can have multiple rooms in a house. Easy peasy lemon squeezy!
A database schema is described in a formal language supported by the database management system (DBMS). In a relational database, the schema defines the tables, the fields in each table, and the relationships between fields and tables. Schemas are generally stored in a data dictionary. Although a schema is defined in text database language, the term is often used to refer to a graphical depiction of the database structure Levels of database schema 1. Conceptual schema, a map of concepts and their relationships 2. Logical schema, a map of entities and their attributes and relations 3. Physical schema, a particular implementation of a logical schema 4. Schema object, Oracle database object 5. Schema is the over all structure of the database
Data independence is the ability to change the schema at one level of the database system without having to change the schema at the other levels.
Database schema are the logical structure of entities (tables or object classes) and their relationships (keys, or object associations) in a database. Schema can exist at different levels of abstraction (see: en.wikipedia.org/wiki/Database_schema). Schema themselves may or may not exist as such in a database. In general schema at the higher levels of abstraction are design models that are captured in printed documents, and authored by business analysts and database designers, rather than created by database programmers and stored in the database itself. But in some types of databases, schema at any level of abstaction can be realized physically. In Oracle databases, schema can be realized as schema objects, which are a part of an Oracle database. These schema objects may represent a human user's conceptual model of the knowledge captured in an enterprise database. Thus defined, there can be many schema that can be associated with one physical database. In other kinds of relational database, an abstract user's schema can be represented by logically linked metadata, views, and stored procedures assocated with a user class. In object-oriented databases, especially those based on the highly self-referential language Smalltalk (e.g. Gemstone/S), schema are realized as "physical" objects in the database as a matter of course, as well as in the logical models captured in design documents. The schema objects in such databases are, in essence, the classes comprising the infrastructure of the database or application. Oracle-style user schema are readily created; these would be realized as user interface orchestrator classes.
Logical data independence refers to the ability to change the conceptual schema without affecting the external schema or application programs. Physical data independence, on the other hand, refers to the ability to change the physical schema without affecting the conceptual schema. This allows changes in the storage structure or access methods without changing how data is viewed or accessed by applications.
The database state refers to the current data stored in the database, including all records and their values. On the other hand, the database schema refers to the structure of the database, including tables, columns, constraints, and relationships. The schema defines how the data is organized and stored in the database.
A starflake schema is a combination of a star schema and a snowflake schema. Starflake schemas are snowflake schemas where only some of the dimension tables have been denormalized. hardkingofflirt@gmail.com
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.