Introduction to database
- 2. Introduction ◦ DBMS stands for Database Management System. ◦ We can break it like this DBMS = Database + Management System. ◦ Database is a collection of data and Management System is a set of programs to store and retrieve those data. ◦ Based on this we can define DBMS like this: DBMS is a collection of inter-related data and set of programs to store & access those data in an easy and effective manner.
- 3. Tables ◦ A table is a collection of data elements organized in terms of rows and columns. ◦ A table is also considered as a convenient representation of relations. But a table can have duplicate row of data while a true relation cannot have duplicate data. Table is the most simplest form of data storage. ◦ Example of an Employee table. ID Name Age Salary 1 Adam 34 13000 2 Alex 28 15000 3 Stuart 20 18000 4 Ross 42 19020
- 4. Entity ◦ Entity is a person, place, thing or event that we want to store information about. ◦ Example: Employee is an entity. ID Name Age Salary 1 Adam 34 13000 2 Alex 28 15000 3 Stuart 20 18000 4 Ross 42 19020
- 5. Records/Row/Tuple ◦ A single entry in a table is called a Tuple or Record or Row. ◦ A tuple in a table represents a set of related data. For example, the above Employee table has 4 tuples/records/rows. ID Name Age Salary 1 Adam 34 13000 2 Alex 28 15000 3 Stuart 20 18000 4 Ross 42 19020 Employee table has 4 tuples/records/rows
- 6. Attributes ◦ A table consists of several records(row), each record can be broken down into several smaller parts of data known as Attributes. ID Name Age Salary 1 Adam 34 13000 2 Alex 28 15000 3 Stuart 20 18000 4 Ross 42 19020 Employee table consist of four attributes, ID, Name, Age and Salary.
- 7. Keys ◦ Keys are used to uniquely identify any record or row of data from the table. ◦ For example: In Student table, ID is used as a key because it is unique for each student. In PERSON table, passport_number, license_number, SSN are keys since they are unique for each person.
- 9. Primary key ◦ It is the first key which is used to identify one and only one instance of an entity uniquely. ◦ An entity can contain multiple keys as we saw in PERSON table. The key which is most suitable from those lists become a primary key. Multiple unique keys
- 10. Candidate Key ◦ A candidate key is an attribute or set of an attribute which can uniquely identify a tuple. ◦ The remaining attributes except for primary key are considered as a candidate key. Candidate key
- 11. Super Key ◦ Super key is a set of an attribute which can uniquely identify a tuple. Super key is a superset of a candidate key. ◦ For example: In the below EMPLOYEE table, for(EMPLOEE_ID, EMPLOYEE_NAME) the name of two employees can be the same, but their EMPLYEE_ID can't be the same. Hence, this combination can also be a key. Super key
- 12. Foreign key ◦ Foreign keys are the column of the table which is used to point to the primary key of another table. ◦ We add the primary key of the DEPARTMENT table, Department_Id as a new attribute in the EMPLOYEE table. ◦ Now in the EMPLOYEE table, Department_Id is the foreign key, and both the tables are related.
- 13. Integrity Constraints ◦ Integrity constraints are a set of rules. It is used to maintain the quality of information. ◦ Integrity constraints ensure that the data insertion, updating, and other processes have to be performed in such a way that data integrity is not affected.
- 14. Domain constraints ◦ Domain constraints can be defined as the definition of a valid set of values for an attribute. ◦ The data type of domain includes string, character, integer, time, date, currency, etc. The value of the attribute must be available in the corresponding domain. ◦ Example:
- 15. Entity integrity constraints ◦ The entity integrity constraint states that primary key value can't be null. ◦ This is because the primary key value is used to identify individual rows in relation and if the primary key has a null value, then we can't identify those rows. ◦ A table can contain a null value other than the primary key field. ◦ Example:
- 16. Referential Integrity Constraints ◦ A referential integrity constraint is specified between two tables. ◦ In the Referential integrity constraints, if a foreign key in Table 1 refers to the Primary Key of Table 2, then every value of the Foreign Key in Table 1 must be null or be available in Table 2.
- 17. Key constraints ◦ Keys are the entity set that is used to identify an entity within its entity set uniquely. ◦ An entity set can have multiple keys, but out of which one key will be the primary key. A primary key can contain a unique and null value in the relational table.
- 18. Schema Architecture ◦ This framework is used to describe the structure of a specific database system. ◦ The three schema architecture is also used to separate the user applications and physical database. ◦ The three schema architecture contains three-levels. It breaks the database down into three different categories.
- 19. Internal Level ◦ The internal level has an internal schema which describes the physical storage structure of the database. ◦ The internal schema is also known as a physical schema. ◦ It uses the physical data model. It is used to define that how the data will be stored in a block. ◦ The physical level is used to describe complex low-level data structures in detail.
- 20. Conceptual Level ◦ The conceptual schema describes the design of a database at the conceptual level. Conceptual level is also known as logical level. ◦ The conceptual schema describes the structure of the whole database. ◦ The conceptual level describes what data are to be stored in the database and also describes what relationship exists among those data. ◦ In the conceptual level, internal details such as an implementation of the data structure are hidden. ◦ Programmers and database administrators work at this level.
- 21. External Level ◦ At the external level, a database contains several schemas that sometimes called as subschema. The subschema is used to describe the different view of the database. ◦ An external schema is also known as view schema. ◦ Each view schema describes the database part that a particular user group is interested and hides the remaining database from that user group. ◦ The view schema describes the end user interaction with database systems.
- 22. Data Independence ◦ Data independence can be explained using the three-schema architecture. ◦ Data independence refers characteristic of being able to modify the schema at one level of the database system without altering the schema at the next higher level.
- 23. Logical Data Independence ◦ Logical data independence refers characteristic of being able to change the conceptual schema without having to change the external schema. ◦ Logical data independence is used to separate the external level from the conceptual view. ◦ If we do any changes in the conceptual view of the data, then the user view of the data would not be affected. ◦ Logical data independence occurs at the user interface level.
- 24. Physical Data Independence ◦ Physical data independence can be defined as the capacity to change the internal schema without having to change the conceptual schema. ◦ If we do any changes in the storage size of the database system server, then the Conceptual structure of the database will not be affected. ◦ Physical data independence is used to separate conceptual levels from the internal levels. ◦ Physical data independence occurs at the logical interface level.
- 25. Need for using DBMS ◦ Processing Queries ◦ Controlling redundancy and inconsistency ◦ Efficient memory management and indexing ◦ Concurrency control and transaction management ◦ Access control and ease in accessing data ◦ Integrity constraints