A conceptual schema is a high-level description of informational needs underlying the design of a database. It typically includes only the main concepts and the main relationships among them. Typically this is a first-cut model, with insufficient detail to build an actual database. This level describes the structure of the whole database for a group of users. The conceptual model is also known as the

data model A data model is an abstract model that organizes elements of data and Standardization, standardizes how they relate to one another and to the properties of real-world Entity, entities. For instance, a data model may specify that the data element ...

that can be used to describe the conceptual schema when a database system is implemented. It hides the internal details of physical storage and targets on describing entities, datatypes, relationships and constraints.

Overview

A conceptual schema or conceptual data model is a map of

concept Concepts are defined as abstract ideas. They are understood to be the fundamental building blocks of the concept behind principles, thoughts and beliefs. They play an important role in all aspects of cognition. As such, concepts are studied by sev ...

s and their relationships used for databases. This describes the semantics of an organization and represents a series of assertions about its nature. Specifically, it describes the things of significance to an organization (''entity classes''), about which it is inclined to collect information, and its characteristics (''attributes'') and the associations between pairs of those things of significance (''relationships''). Because a conceptual schema represents the semantics of an organization, and not a database design, it may exist on various levels of abstraction. The original

ANSI The American National Standards Institute (ANSI ) is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organi ...

four-schema architecture began with the set of ''external schemata'' that each represents one person's view of the world around him or her. These are consolidated into a single ''conceptual schema'' that is the superset of all of those external views. A data model can be as concrete as each person's perspective, but this tends to make it inflexible. If that person's world changes, the model must change. Conceptual data models take a more abstract perspective, identifying the fundamental things, of which the things an individual deals with are just examples. The model does allow for what is called

inheritance Inheritance is the practice of receiving private property, titles, debts, entitlements, privileges, rights, and obligations upon the death of an individual. The rules of inheritance differ among societies and have changed over time. Officiall ...

in object oriented terms. The set of instances of an entity class may be subdivided into entity classes in their own right. Thus, each instance of a ''sub-type'' entity class is also an instance of the entity class's ''super-type''. Each instance of the super-type entity class, then is also an instance of one of the sub-type entity classes. Super-type/ sub-type relationships may be '' exclusive'' or not. A methodology may require that each instance of a super-type may ''only'' be an instance of ''one'' sub-type. Similarly, a super-type/sub-type relationship may be ''exhaustive'' or not. It is exhaustive if the methodology requires that each instance of a super-type ''must be'' an instance of a sub-type. A sub-type named "Other" is often necessary.

Example relationships

* Each PERSON may be ''the vendor in'' one or more ORDERS. * Each ORDER must be ''from'' one and only one PERSON. * PERSON is ''a sub-type of'' PARTY. (Meaning that every instance of PERSON is also an instance of PARTY.) * Each EMPLOYEE may have a ''supervisor'' who is also an EMPLOYEE.

Data structure diagram

A data structure diagram (DSD) is a data model or diagram used to describe conceptual data models by providing graphical notations which document entities and their relationships, and the constraints that bind them.

References

External links

* A differen
point of view
as described by the agile community {{DEFAULTSORT:Conceptual Schema Data modeling Concepts

Overview

Example relationships

Data structure diagram

See also

References

Further reading

External links