Explain about the Physical Data Model?

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Explain about the Physical Data Model?..

A physical data model (a.k.a. database design) is a
representation of a data design which takes into account the
facilities and constraints of a given database management
system. In the lifecycle of a project it is typically
derived from a logical data model, though it may be
reverse-engineered from a given database implementation. A
complete physical data model will include all the database
artifacts required to create relationships between tables or
achieve performance goals, such as indexes, constraint
definitions, linking tables, partitioned tables or clusters.
The physical data model can usually be used to calculate
storage estimates and may include specific storage
allocation details for a given database system.

The Physical Data Model (PDM) describes how the information
represented in the Logical Data Model is actually
implemented, how the information-exchange requirements are
implemented, and how the data entities and their
relationships are maintained.
There should be a mapping from a given Logical Data Model to
the Physical Data Model if both models are used. The form of
the Physical Data Model can vary greatly. For some purposes,
an additional entity-relationship style diagram will
suffice. The Data Definition Language (DDL) may also be
used. References to message format standards (which identify
message types and options to be used) may suffice for
message-oriented implementations. Descriptions of file
formats may be used when file passing is the mode used to
exchange information. Interoperating systems may use a
variety of techniques to exchange data, and thus have
several distinct partitions in their Physical Data Model
with each partition using a different form.