What is the difference between a logical data model and a physical database design?
| Logical Model | Physical Database Design |
| Includes all entities, relationships, and attributes (and their information types) whether or not supported by a technology. | Includes tables, columns, keys, data types, and validation rules. DB triggers, stored procedures, domains, and access constraints(security). |
| Uses business names. | Names may be limited by the DBMS. |
| Captures and records information necessary for the business. | Includes technology-specific data elements such as flags, switches, and timestamps. |
| Includes unique identifiers. | Includes primary keys, foreign keys, and indices for faster data access. |
| Is normalized to at least 3rd normal form. | May be de-normalized to meet performance requirements. |
| Does not include any redundant data. | May include redundant data elements. |
| Does not include any derived data. | May include results of complex or difficult to recreate calculations. |
| Business experts drive the model. | DBA drive the model. |
What happens if you don’t build a logical data model?
The database design task is a much longer activity and the database may be poorly structured. Since not all business data requirements have been thoroughly flushed out, database designs are unstable throughout the development process.
During coding, testing and even in implementation, developers are finding additional data elements, requiring the DBAs to be re-active instead of pro-active. Resulting databases may be poorly structured, looking like a patchwork quilt, instead of being well planned which will be easy to maintain. Errors in the database design will cause the entire system to be unusable.
[Thanks to Anil Khatwad for submitting this useful article on Logical Data Modeling!]
3. What is Data Architecture?
[Submitted by: Anil Khatwad, Miramar, Florida, United States.]
Data architecture is an orderly arrangement of parts to do four things: organize, store, access and move data. If organizations don't have the data architecture right, it's hard to get anything else right.
In this articale, I want to discuss the scope of data architecture. In subsequent columns I will address planning and design issues that the data architect is expected to solve.
What is Data Architecture?In the IT world, "architecture" refers to an orderly arrangement of parts. Thus, data architecture is an orderly arrangement of parts to do four things: organize, store, access and move data. Of course, a typical solution involving corporate data does a lot more than four things, but every action performed by the solution fits into one of these four categories. Think of these categories as the four suits that make up the data architecture "deck."
What is Data Architecture? - Continued.....
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