Schema in dbms

In this article Applies to: This topic describes how to create a schema in SQL Server by using SQL Server Management Studio or Transact-SQL. Before You Begin Limitations and Restrictions • The new schema is owned by one of the following database-level principals: database user, database role, or application role. Objects created within a schema are owned by the owner of the schema, and have a NULL principal_id in sys.objects. Ownership of schema-contained objects can be transferred to any database-level principal, but the schema owner always retains CONTROL permission on objects within the schema. • When creating a database object, if you specify a valid domain principal (user or group) as the object owner, the domain principal is added to the database as a schema. The new schema is owned by that domain principal. Security Permissions • Requires CREATE SCHEMA permission on the database. • To specify another user as the owner of the schema being created, the caller must have IMPERSONATE permission on that user. If a database role is specified as the owner, the caller must meet one of the following criteria: membership in the role or ALTER permission on the role. Using SQL Server Management Studio To create a schema • In Object Explorer, expand the Databases folder. • Expand the database in which to create the new database schema. • Right-click the Security folder, point to New, and select Schema. • In the Schema - New dialog box, on the General page, enter a name for the ne...

The database schema is the structure of a [ citation needed] These integrity constraints ensure compatibility between parts of the schema. All constraints are expressible in the same language. A database can be considered a structure in realization of the "A database schema specifies, based on the A database generally stores its schema in a In an Ideal requirements for schema integration [ ] The requirements listed below influence the detailed structure of schemas that are produced. Certain applications will not require that all of these conditions are met, but these four requirements are the most ideal. Overlap preservation Each of the overlapping elements specified in the input mapping is also in a database schema relation. Extended overlap preservation Source-specific elements that are associated with a source’s overlapping elements are passed through to the database schema. Normalization Independent entities and relationships in the source data should not be grouped together in the same relation in the database schema. In particular, source specific schema elements should not be grouped with overlapping schema elements, if the grouping co-locates independent entities or relationships. Minimality If any elements of the database schema are dropped then the database schema is not ideal. Example of two schema integrations [ ] Suppose we want a mediated schema to Go-travel has two relations: Flight(flight-number, date, time, price) Oracle database specificity [ ] In the con...

A schema diagram, as shown above, displays only names of record types (entities) and names of data items (attributes) and does not show the relationships among the various files. The schema will remain the same while the values filled into it change from instant to instant. When the schema framework is filled in with data item values, it is referred as an instance of the schema. The data in the database at a particular moment of time is called a database state or snapshot, which is also called the current set of occurrences or instances in the database In other words, “the description of a database is called the database schema, which is specified during database design and is not expected to change frequently”. A displayed schema is called a schema diagram. A schema diagram displays only some aspects of a schema, such as the name of record types and data items, and some types of constraints. Other aspects are not specified in the schema diagram. It does not specify the Sub schema A sub schema is a subset of the schema and inherits the same property that a schema has. The plan (or scheme) for a view is often called sub schema. Sub schema refers to an application programmer’s (user’s) view of the data item types and record types, which he or she uses. It gives the users a window through which he or she can view only that part of the database, which is of interest to him. Therefore, different application programs can have different view of data.

I was just starting with reading a book about databases and encountered schemas and data models. I read that schema is the structural design of a database and data model is a set of conceptual tools to describe the data and the relationships like Er model etc. I don't get the real sense of difference between the two. Is schema actually a file in Dbms and data model is just a concept? A schema is collection of database objects that are logically grouped together. These can be anything, tables, views, stored procedure etc. Schemas are typically used to logically group objects in a database. For example, an application that has reporting and auditing components may have 2 schemas called reporting and auditing with a collection of tables, stored procedures etc. With Schemas, one can segregate out the reporting objects and audit objects. One can also create different security accounts which can only access a specific schema. A fully qualified name will include the schema. For example: SELECT * FROM [Test].[dbo].[Person] Test is the database. dbo is the schema. Person is the table. A data model in a database should be relational which means it is described by tables. The data describes how the data is stored and organized. A data model may belong to one or more schemas, typically usually it just belongs to one schema. The person table will be a part of a number of tables and relations that make up the data model. In fact the words are often basically interchangeable. In SQL Serv...

Schema is a logical description of the entire database. It includes the name and description of records of all record types including all associated data-items and aggregates. Much like a database, a data warehouse also requires to maintain a schema. A database uses relational model, while a data warehouse uses Star, Snowflake, and Fact Constellation schema. In this chapter, we will discuss the schemas used in a data warehouse. Star Schema • Each dimension in a star schema is represented with only one-dimension table. • This dimension table contains the set of attributes. • The following diagram shows the sales data of a company with respect to the four dimensions, namely time, item, branch, and location. • There is a fact table at the center. It contains the keys to each of four dimensions. • The fact table also contains the attributes, namely dollars sold and units sold. Note− Each dimension has only one dimension table and each table holds a set of attributes. For example, the location dimension table contains the attribute set : Syntax for Dimension Definition define dimension as ( ) Star Schema Definition The star schema that we have discussed can be defined using Data Mining Query Language (DMQL) as follows − define cube sales star [time, item, branch, location]: dollars sold = sum(sales in dollars), units sold = count(*) define dimension time as (time key, day, day of week, month, quarter, year) define dimension item as (item key, item name, brand, type, supplier...

In this article Applies to: A core concept of SQL Server security is that owners of objects have irrevocable permissions to administer them. You can't remove privileges from an object owner, and you can't drop users from a database if they own objects in it. User-schema separation User-schema separation allows for more flexibility in managing database object permissions. A schema is a named container for database objects, which allows you to group objects into separate namespaces. For example, the AdventureWorks sample database contains schemas for Production, Sales, and HumanResources. The four-part naming syntax for referring to objects specifies the schema name. Server.Database.DatabaseSchema.DatabaseObject Schema owners and permissions Schemas can be owned by any database By default, when developers create objects in a schema, the objects are owned by the security principal that owns the schema, not the developer. Object ownership can be transferred with Built-in schemas for backward compatibility SQL Server ships with nine pre-defined schemas that have the same names as the built-in database users and roles: db_accessadmin, db_backupoperator, db_datareader, db_datawriter, db_ddladmin, db_denydatareader, db_denydatawriter, db_owner, db_securityadmin. These exist for backward compatibility. The recommendation is to not use them for user objects. You can drop the schemas that have the same names as the fixed database roles - unless they're already in use, in which case t...