How is the hierarchical data model different from the network data model?

The hierarchical data model and the network data model are both early database models that preceded the relational model. They have distinct structures and ways of representing relationships within a database. Here are the key differences between the hierarchical and network data models:

Hierarchical Data Model:

1. Structure:

   • Tree-Like Structure: In the hierarchical model, data is organized in a tree-like structure with a single root representing the entire database. Each node in the tree can have multiple child nodes, but each child has only one parent.

2. Relationships:

   • One-to-Many Relationships: Relationships are represented using a one-to-many structure. A parent node can have multiple child nodes, but each child has only one parent.

3. Access Path:

   • Single Access Path: Retrieving data in a hierarchical model typically involves following a single access path from the root to the desired node. It is efficient for certain types of queries but can be limiting for others.

4. Example:

   • Example Database: A file system is an example of a hierarchical database where directories (folders) contain files, and each directory can contain subdirectories.

Network Data Model:

1. Structure:

   • Graph-Like Structure: The network model is more flexible than the hierarchical model and uses a graph-like structure. It allows nodes to have multiple parents and children, creating a network of interconnected records.

2. Relationships:

   • Many-to-Many Relationships: Relationships in the network model are represented as many-to-many. Each record (node) can have multiple parent and child records, allowing for more complex relationships.

3. Access Path:

   • Multiple Access Paths: The network model allows for multiple access paths to retrieve data. This flexibility in navigation makes it more powerful for certain types of queries compared to the hierarchical model.

4. Example:

   • Example Database: The CODASYL (Conference on Data Systems Languages) database management system is an example of a network database. In this model, records (nodes) can be connected in various ways, enabling more complex relationships between entities.

Key Differences:

1. Flexibility:

   • The hierarchical model is more rigid, with a strict parent-child relationship, while the network model provides more flexibility with many-to-many relationships.

2. Access Paths:

   • The hierarchical model typically follows a single access path, whereas the network model supports multiple access paths, making it more versatile for querying.

3. Complexity:

   • The network model allows for more complex relationships, making it suitable for scenarios where entities have intricate connections.

4. Use Cases:

   • The hierarchical model is often used in scenarios where data naturally fits a tree structure, such as organizational charts or file systems. The network model is used in cases where relationships are more diverse and complex, such as in scientific or engineering applications.

It's important to note that both the hierarchical and network data models have limitations, and they have been largely superseded by the relational model, which offers a more straightforward and intuitive way to represent data and relationships.