I can see physical and conceptual modelling as same. Whatever we need for conceptual modelling will be present in physical modelling.
Please explain what is the purpose of conceptual modelling?
The purpose of a conceptual model is to provide a high level understanding of the entire model in a concise form that can be understood by business analysts and Subject Mater Experts (SME) in about a day. Think of an enterprise wide model in 3 levels:
Level 1: 30,000 foot view - Subject Area Model - 12 entities - for management overview
Level 2: 10,000 foot view - Conceptual Model - 200 entities - for overall Subject Mater Expert
Level 3: On the ground view - Detail model - thousands of entities - for modeler, DBA, Subject model expert for one particular subject
The conceptual model lays out each topic of the model in enough detail for the reader to grasp each topic covered and the basic relationships which join the topics together. A model with a couple hundred entities can be reviewed in a day and understood in sweeping business terms. A detail enterprise model takes months or years to fully consume. A subject area model takes an hour to consume.
If the detail model is less than enterprise wide, say financial topics only, then the content shifts but I think the entity count could remain about the same in each level. The multiple levels provide a drill down to aid in learning the model. When I educate a client on our model I always start at the subject level and work down. Each level gives a level of understanding that provides a framework on which to hang the next deeper level of understanding.
Conceptual model represents mostly the business needs. It is usually business questions list and matrix. It serves as input to the Logical data model which is a business solution. Conceptual model concentrates on analysis process with lots of uncertainties where business requirements are more on the agenda.
Thanks and regards,