Introduction: In data base systems design, (under Security Design), we must identify different user groups and different roles played by various users. For each role, and user group
Download 119.63 Kb.
|
- Navigate this page:
- An attribute
- A relationship
- A cardinality
| Introduction: In data base systems design, (under Security Design), we must identify different user groups and different roles played by various users. For each role, and user group, we also have to identify the parts of the database that they must be able to access. For the purpose of this question, these include but not limited to: An entity An attribute A relationship and A cardinality. An entity It is a collection of objects. An entity is an object that is distinguishable from other objects by a set of attributes. An entity may be an 'object' with a physical existence. In database administration, an entity can be a single place, or object. In an E-R Model, it is a 'thing' in the real world with an independent existence. Data can be stored in such entities in which entities consist of attributes that define their characteristic features. Examples of entities; places like schools, hospitals among others. According to the diagram above, an entity is the orchard because it consists of the attributes- apples and the apple trees which define its characteristics. An attribute Attributes in relational databases, are defined as the describing characteristics or properties that define all items pertaining to a certain category applied to all cells of a column, and represent data sets applied to a single entity to uniquely identify each item. Can also mean an object closely associated with or belonging to a specific thing or office, an office being the attribute of an organization: such an object used for identification in painting or sculpture it is to define the characteristics of an entity. Characteristics of an entity are called attributes. According to the diagram, the attribute is an apple which defines the characteristic of an orchard. A relationship A relationship, in the context of databases, is a situation that exists between two relational database tables when one table has a foreign key that references the primary key of the other table. Relationships allow relational databases to split and store data in different tables, while linking disparate data items. A relationship is a state of connectedness between people or things. According to the diagram, a relationship’s an apple tree which defines that connectedness between an orchard and an apple. And also an apple tree has a relationship with an orchard because many apple trees turn out in an orchard. A cardinality Cardinality is a mathematical term. It translates into the number of elements in a set. In databases, cardinality refers to the relationships between the data in two database tables. Cardinality defines how many instances of one entity are related to instances of another entity. According to the diagram the cardinality denotes a one-to-one relationship; A relationship between an apple to an apple tree. A relationship between an apple to an orchard. The role that cardinality plays must not be underestimated when defining the relationships between database entities represented as database tables and columns. In summary, the three cardinalities (the one-to-one, one-to-many, and many-to-many relationships) are fundamental to describing the relationships between different objects or entities. References; Class notes by Ms. MUGABIRWE BEATRICE. bmc.com/blogs/dba-database-administrator/ https://personal.utdallas.edu/~bhavani.thuraisingham/Publications/Journal- Papers/DAS/J1_Multilevel_Security_in_Database_Management_Systems.pdf https://www.ibm.com/cloud/learn/database-security. Download 119.63 Kb. Share with your friends:
|