In systems engineering and database development, creating a logical data model (LDM) is the second step in creating the entire data model, coming after the conceptual data model (CDM) and proceeded by the physical data model (PDM). In the logical data model, engineers target the important data for the business and show the entire database’s relationship from one section to another. The LDM diagram will show different tables with data titles, but the actual data will not be present. For example, if a date table is made, the LDM diagram will show titles such as “Month” and “Year,” but the actual month and year values will not be present.
When it comes to data mapping, the first model is the CDM. This diagram is a simple concept that starts off the data modeling. There will be several tables, without any titles in them, and there may be some lines to show relationships.
After the conceptual model, the logical data model is made. This model is much more detailed in terms of both titles and relationships. The blank tables are filled with arbitrary values so engineers know what data is important. For example, the conceptual model will have a table named “Store,” while the LDM will fill the table with titles such as “Store Description” and “Store Name.” The data is not implemented at this stage, which intends only to let the engineers know what information is required for a functioning database.
The relationships between the different tables also are detailed, so engineers will know how to make them interact. There is usually one central table, to which all other tables connect. Between the ancillary tables, there are sometimes interconnections, showing that these tables cannot function independently of one another. Lines connecting one table to another show these relationships.
A logical data model is needed for many reasons. It clarifies what information the business is collecting and how all the data are related. This also makes it easier for management to look through the draft and see if more information is needed. The information is diagramed, so the engineers will need less time to create the data model, because the plan is detailed and there is no guesswork.
After the logical data model, the PDM is created. This is the real and physical implementation of the database. In this model, all the arbitrary values are filled with real values, such as “Year” being filled with “2011,” and the data are actually used and being collected.