際際滷

際際滷Share a Scribd company logo

Er model

Download as PPTX, PDF
Umair Shakir
Umair Shakir

The document discusses key concepts in database development including: - The conceptual and physical levels of a database, with the conceptual being objects like tables and the physical being files on a hard disk. - Common data models like the entity relationship model and relational model that describe organizational data through entities, attributes, and relationships. - Key entities include objects an organization wants to track like students, employees, and departments.

1 of 7
Download to read offline
Muhammad Umair Oracle Database 11g Developer Track
Database Creation Developers creates database conceptually, whereas DBMS creates database physically. At conceptual level, database is consisting of a set of objects (like tables) whereas at physical level database is a set of files on hard disk Data Model A set of concepts used to describe data of a organization at a higher level
Entity Relationship Model (ER Model) A data model used to describe data of an organization in the form of entities and their association Relational Model A data model used to describe data of an organization in the form of relations Physical Data Model A data model that is at the lowest level and can be converted to DBMS language directly
Entity A group of objects having some characteristics about which an organization wants to maintain data e.g. Students, Employee, Departments, Faculty, courses, lab, Library, degree etc. Entity can be person, place, thing, event or a concept. Entity Instance Single occurrence of a Entity
Attribute An attribute is a characteristic of an entity about which organization is interested Types of Attributes Composite Attribute An attribute that is divided into more attributes e.g. Date of birth can be divided into day, month, year. Qualification can be divided into degree-name, university, passing year, %age
Simple Attribute An attribute that can not divided into more attributes e.g. Gender (Male/Female), Salary Multi-valued Attributes An attribute that can hold more then one value for a single entity instance e.g. Cell no, email-id, Experience, Qualification etc. Single-valued Attributes An attribute that can not hold more then one value for a single entity instance e.g. Father name, Salary, Gender, Designation etc.
Derived Attribute An attribute that is not necessary to be stored on hard disk because its value can be calculated from some other attribute e.g. Age can be calculated from date of birth, GPA can be calculated from marks. Non-Derived Attribute An attribute that is necessary to be stored on hard disk because its value can not be calculated from some other attribute e.g. Father Name etc.

More Related Content

Er model

  • 1. Muhammad Umair Oracle Database 11g Developer Track
  • 2. Database Creation Developers creates database conceptually, whereas DBMS creates database physically. At conceptual level, database is consisting of a set of objects (like tables) whereas at physical level database is a set of files on hard disk Data Model A set of concepts used to describe data of a organization at a higher level
  • 3. Entity Relationship Model (ER Model) A data model used to describe data of an organization in the form of entities and their association Relational Model A data model used to describe data of an organization in the form of relations Physical Data Model A data model that is at the lowest level and can be converted to DBMS language directly
  • 4. Entity A group of objects having some characteristics about which an organization wants to maintain data e.g. Students, Employee, Departments, Faculty, courses, lab, Library, degree etc. Entity can be person, place, thing, event or a concept. Entity Instance Single occurrence of a Entity
  • 5. Attribute An attribute is a characteristic of an entity about which organization is interested Types of Attributes Composite Attribute An attribute that is divided into more attributes e.g. Date of birth can be divided into day, month, year. Qualification can be divided into degree-name, university, passing year, %age
  • 6. Simple Attribute An attribute that can not divided into more attributes e.g. Gender (Male/Female), Salary Multi-valued Attributes An attribute that can hold more then one value for a single entity instance e.g. Cell no, email-id, Experience, Qualification etc. Single-valued Attributes An attribute that can not hold more then one value for a single entity instance e.g. Father name, Salary, Gender, Designation etc.
  • 7. Derived Attribute An attribute that is not necessary to be stored on hard disk because its value can be calculated from some other attribute e.g. Age can be calculated from date of birth, GPA can be calculated from marks. Non-Derived Attribute An attribute that is necessary to be stored on hard disk because its value can not be calculated from some other attribute e.g. Father Name etc.