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What are the types of physical data models? Explain them.Flat-file: A flat file describes a table as a plain text file. It can be a mixed text or binary file as well where 1 line represents one record. Various fields exist in a single line and are delimited using a symbol like comma or semicolon.
Hierarchical: Data is stored in a hierarchical or tree like structure. The whole model is a collection of parent-child relationships, where every parent can have multiple children but every child must have a single parent. All entities/tables are arranged in such a hierarchical way. Every single row represents a record and fields are depicted as columns.
Relational: Is mainly based on first-order predicate logic proposed by Codd. A database is depicted as a collection of predicates with various constraints, possible values, relationships and value boundaries. It provides a way for specifying data and queries.
Object-Oriented: Object oriented model is based around various physical entities termed as objects, their attributes, behavior and relationships. Every object is a table and all object attributes are converted to table fields. Relationships among objects decide foreign keys in the database.
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