Question

1 .differenate b/w hierarchical ,network and relation models

Answer 1

• Simpler to use: The Hierarchical databases use the logical parent-child relationship and it looks simpler as well. But Relational databases involve tables to store records in the form of table fields. Also in most cases, it requires a unique key for each record.

•  Which is older? The Hierarchical databases came into existence even before the Relational databases and it is the processor to all the other databases.

• The Fundamental difference in the data notion: In hierarchical databases, a category of data is termed as ‘Segments’ whereas in Relational databases it is termed as ‘Fields’.

• Inheritance: Every child segment/node in a hierarchical database, inherits the properties of its parent. But in relational databases, there is no concept of inheritance as there are no levels of data.

• Data Linking: In hierarchical databases, the Segments are implicitly linked as a child is linked to its parent. But in relational databases, we should explicitly link the tables with the help of ‘Primary keys’ and ‘Foreign keys’.

• Use of keys: The relational databases are generally framed with unique keys called the Primary key and also keys from other tables called the Foreign keys. These foreign keys are primary keys in some other table and it is referred while accessing the other table from this table. So, the main use of keys is to give a unique identification to the data records and to refer other tables during the data fetching process. But a hierarchical database never uses keys. It has its links to denote the path to be traversed during the data fetch. Therefore, we can consider the keys in relational databases as the equivalent of the paths in hierarchical databases during data fetches. But the paths never represent the uniqueness of data that has been stored in hierarchical databases.

• Unique & Duplicate data: As the keys represent the uniqueness of data in relational databases, we can easily list such data on demand. But when the same is required in a hierarchical database, it needs a lots processing. We can have more than one copy of the same book in a library but assigned with different book numbers. In this case, we should compare the book names to identify the duplicates. Therefore, relational databases are suited to store unique data whereas hierarchical databases are good ones for data with duplicates.

• Data Fetching: Just imagine that you have a library management system and it stores book details with an assigned book number for each bo

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