What is a view in database system and how it is related to data independence?
View is a table that does not really exist in its own right, it derived from one or more underlying base table. In other word view is a virtual table. There is no stored file that direct represents view.
- Views can represent a subset of the data contained in a table.
- View perform alogical operations.
- View can join multiple table in a single vertual table.
- Importent feature is, to hide complexity of data.
Now disscuss how view relate data independence, restructuring of base tables is not reflected in views. Thus the view can insulate users from the effects of restructuring and growth in the database. Hence accounts for logical data independence.Reply
What is Data Independence in Database System?
Data independence means that, the ability to modify the schema definition in one level should not affect the schema definition in the next higher level. The application is independent of the storage structure and access strategy of data.
Two types of Data Independence are:
1. Logical Data Independence: It is more difficult to achieve. Modification in logical level should affect the view level.
2. Physical Data Independence: Modification in physical level should not affect the logical level.
What is extension and intension?
Extension: It is the number of tuples(row) present in a table at any instance. This is time dependent.
It is a constant value that gives the:
2. Structure of table
3. The constraints laid on it. Reply
Describe levels of Abstraction in Database?
1. Physical Level:Physical level is the lower level of abstraction.Its define how data is stored in database.
2. Logical Level:The next higher level of abstraction, its describe what data be store and each logical operation done at this level, links and concept apply here.
3. View Level:This is the higher level describe only part of entire database.Reply
Disadvantage of File Processing System or Advantage of Database over File Processing System ?
1. Data redundancy and consistency:Not easily in File System but in database possible.
2. Difficalty to accessing data:In database easily done.
3. Data isolation:Database provided but in File System not.
4. Data integrity:Database provided but in File System not.
5. Concurrent access is not possible:Database provided but in File System not.
6. Security Problems:Database provided but in File System not.Reply
Explain about relational database?
1. Data represent in form of coloumn and row, coloumn means attribute and row means touples present instance of data.
2. This Database model came into existence with help of mathematical concepts.
3. Using some other concepts like normalization, touple relational calculus.Reply
Explain about Network model?
This model provides greater flexibility and easy access to data.This model provide logical relationship among many parent database.But implimenting this model is more difficult due to time consuming and cost. Its flexible because through link easily accesesing of information.Reply
Explain about the hierarchical model of database?
The word hierarchi means tree form relationship,like a tree with branches.Means Relationship formed like tree structure in a database called hierarchical model.With this database you form relationship among many tables with certain concept.It has a downward link to describe the nesting and they are arranged in a particular order down the same level of the list. Reply
Explain about XML databases?
XML databases came into existence in 2000. This database lets you organize data irrespective of whether it is organized or not.This data can exported and serialized into the desired format.
Two major classes of XML database exist:
2. Native XMLReply
Explain about object oriented databases?