crypyography
QNS: Discuss the characteristics of relations that make them different fromordinary tables and files.
Ans:Tables and files have some particular order but relations don’t. ordinary tablesand files are static while a relational database has data thatis dependent on the data that is entered in tuples that are related to thatattribute. in the ordinary tables and files, there are no constraintsrelated to the related data and a user could input whatever they wanted
Q. Discuss the various reasons that lead to the occurrence of null values in relations in detail?
Each value in a tuple is an atomic value; that is, it is not divisible into components within the framework of the basic relational model. Hence, composite and multivalued attributes are not allowed. This model is sometimes called the flat relational model. Much of the theory behind the relational model was developed with this assumption in mind, which is called the first normal form assumption. Hence, multivalued attributes must be represented by separate relations, and composite attributes are represented only by their simple component attributes in the basic relational model.
An important concept is that of nulls, which are used to represent the values of attributes that may be unknown or may not apply to a tuple. A special value, called null, is used for these cases. In general, we can have several meanings for null values, such as "value unknown," "value exists but is not available," or "attribute does not apply to this tuple." It is possible to devise different codes for different meanings of null values. Incorporating different types of null values into the relational model operations has proven difficult and is outside the scope of our presentation.
If an instance (tuple) of a relation lacks having that attribute. i.e: a student that does not have a mobile phone or an office phones. The values for these attribute for that particular student will be null. It is important to note that a null
Ans:Tables and files have some particular order but relations don’t. ordinary tablesand files are static while a relational database has data thatis dependent on the data that is entered in tuples that are related to thatattribute. in the ordinary tables and files, there are no constraintsrelated to the related data and a user could input whatever they wanted
Q. Discuss the various reasons that lead to the occurrence of null values in relations in detail?
Each value in a tuple is an atomic value; that is, it is not divisible into components within the framework of the basic relational model. Hence, composite and multivalued attributes are not allowed. This model is sometimes called the flat relational model. Much of the theory behind the relational model was developed with this assumption in mind, which is called the first normal form assumption. Hence, multivalued attributes must be represented by separate relations, and composite attributes are represented only by their simple component attributes in the basic relational model.
An important concept is that of nulls, which are used to represent the values of attributes that may be unknown or may not apply to a tuple. A special value, called null, is used for these cases. In general, we can have several meanings for null values, such as "value unknown," "value exists but is not available," or "attribute does not apply to this tuple." It is possible to devise different codes for different meanings of null values. Incorporating different types of null values into the relational model operations has proven difficult and is outside the scope of our presentation.
If an instance (tuple) of a relation lacks having that attribute. i.e: a student that does not have a mobile phone or an office phones. The values for these attribute for that particular student will be null. It is important to note that a null