Schema Diagrams




A database schema, along with primary key and foreign key dependencies, can be depicted by schema diagrams. Figure 2.8 shows the schema diagram for our university organization. Each relation appears as a box, with the relation name at the top in blue, and the attributes listed inside the box. Primary key attributes are shown underlined. Foreign key dependencies appear as arrows from the foreign key attributes of the referencing relation to the primary key of the referenced relation.

Schema Diagrams

 

Referential integrity constraints other than foreign key constraints are not shown explicitly in schema diagrams. Entity relationship diagrams let us represent several kinds of constraints, including general referential integrity constraints.Many database systems provide design tools with a graphical user interface for creating schema diagrams. 



Frequently Asked Questions

+
Ans: XML (Extensible Markup Language)—has emerged as the standard for structuring and exchanging data over the Web. XML can be used to provide information about the structure and meaning of the data in the Web pages rather than just specifying how the Web pages are formatted for display on the screen view more..
+
Ans: Object databases is the power they give the designer to specify both the structure of complex objects and the operations that can be applied to these objects view more..
+
Ans: This chapter discusses techniques for securing databases against a variety of threats. It also presents schemes of providing access privileges to authorized users. view more..
+
Ans: A database schema, along with primary key and foreign key dependencies, can be depicted by schema diagrams. view more..
+
Ans: A query language is a language in which a user requests information from the database. view more..
+
Ans: All procedural relational query languages provide a set of operations that can be applied to either a single relation or a pair of relations. view more..
+
Ans: An object database is a database management system in which information is represented in the form of objects as used in object-oriented programming. Object databases are different from relational databases which are table-oriented. Object-relational databases are a hybrid of both approaches. view more..
+
Ans: IBM developed the original version of SQL, originally called Sequel, as part of the System R project in the early 1970s. view more..
+
Ans: The set of relations in a database must be specified to the system by means of a data-definition language (DDL). view more..
+
Ans: The basic structure of an SQL query consists of three clauses: select, from, and where. view more..
+
Ans: This chapter discusses techniques for securing databases against a variety of threats. It also presents schemes of providing access privileges to authorized users. view more..
+
Ans: The natural join operation operates on two relations and produces a relation as the result. view more..
+
Ans: Reason to rename a relation is a case where we wish to compare tuples in the same relation. view more..
+
Ans: SQL permits a variety of functions on character strings. Read to know about them. view more..
+
Ans: The company is organized into departments. Each department has a unique name, a unique number, and a particular employee who manages the department. We keep track of the start date when that employee began managing the department. A department may have several locations.  A department controls a number of projects, each of which has a unique name, a unique number, and a single location view more..
+
Ans: Entities and Their Attributes. The basic object that the ER model represents is an entity, which is a thing in the real world with an independent existence. An entity may be an object with a physical existence (for example, a particular person, car, house, or employee) view more..
+
Ans: A database usually contains groups of entities that are similar. For example, a company employing hundreds of employees may want to store similar information concerning each of the employees. These employee entities share the same attributes, but each entity has its own value(s) for each attribut view more..
+
Ans: An entity type DEPARTMENT with attributes Name, Number, Locations, Manager, and Manager_start_date. Locations is the only multivalued attribute. We can specify that both Name and Number are (separate) key attributes because each was specified to be unique view more..




Rating - 3/5
513 views

Advertisements