Toad Data Modeler allows you to design and maintain a logical model giving a complete picture of the business area. Logical model is independent of the database platform and is much simpler than physical model. It uses objects such as inheritance, valid values or M:N relationships. From the Logical ER (LER) diagram, you can build a Physical ER (PER) diagram of the selected database platform (LER to PER conversion).

Note:

This topic contains information on objects and functions that are specific for logical modeling. General information and other features applicable in Logical model as well as in Physical model are contained and described in other sections of this Help file. See e.g. the "Model Objects" chapter, "Model Explorer" topic etc.
See the sample logical model Employee that is included in the installation package for Toad Data Modeler. Default location is: C:\Program Files\Quest Software\Toad Data Modeler\Samples.

To create a logical model

Select File | New | Model |Logical Data Model tab.

Benefits of Logical Data Model

Logical Data Model allows you to model inheritances in entity relationship diagrams. Universal Data Model and Physical Data Model do not support this feature.

Specifics of Logical Data Model

There are three methods how inheritance can be resolved when converting to physical model.
Attributes do not migrate to child entities.
It is not possible to define database specific items in Logical Model, for example sequences/autoincrements etc.
You can define Valid Values in logical model (will be converted to physical model).

Benefits of Super and Sub Types

In Logical Model you can define database structure in various ways. See the pictures below. Both of them show a structure modeled in Logical Model and both the models will result in the identical output when converted to Physical Model. The difference is that Model A uses Super and Sub Types while Model B doesn't use inheritance at all.

Model A - Utilizing Super and Sub Types

Model B - Lacking Super and Sub Types

This example shows:

That you can create logical models in different ways and achieve the same result after conversion to physical model.
That you can be more productive when using inheritance. For example, you only need to change the Last Name attribute once in the first model. Without using inheritance in model B, you have to change it four times.
How much “readable” the first model is compared to the second one.
How important is to select appropriate inheritance resolution when converting your logical model to physical.
That creating logical models without inheritance has minimal benefits compared to using inheritance.

Disadvantage

The main disadvantage of logical modeling is that direct synchronization with existing database is not possible. Only physical models of specific database platforms and versions may be synchronized with an existing database. Therefore, if you want to synchronize your logical model, you need to convert it to the physical model first.

Toad Data Modeler allows you to convert your logical model to a physical model of any supported database system.

Note:

Before you convert your Logical model to Physical model, you should be aware of the following:

Physical model supports only non-identifying self relationship.
Inheritance is not supported in PER model. Toad Data Modeler solves this by converting Inheritance object into either Single Table, N-1 Tables or N Tables. See Inheritance.
Keys in LER models do not migrate.
You can select a linking method in LER model.
M:N relationships are supported in both models.
Before you start the conversion, you can set up the conversion rules in the Data Type Conversion Settings dialog. This option is available only if Expert Mode is enabled.
Cycled relationships will be ignored during LER to PER conversion and will not be converted. A message informing you about this will be displayed in Message Explorer Log.

Select your desired database platform.

Change any of the conversion settings, if necessary.

Choose what object types will be converted. You can access full list of Objects and Properties by clicking on Detailed Settings.

Check items you want to convert to another model. For easier item management use buttons located on the top.

Review the statistic and when you're done, click the Finish button.
After a short while your Logical model will be converted to Physical model of your desired database platform.

TIP:If you plan to do this action again in the future, you might want to click the Save Action button to save this Action Definition. See Model Actions for more information.

Selection Tree Overview

	Collapse All.
	Import selection from a saved file.
	Save selection to a file.
	Checks all items.
	Unchecks all items.
	Opens the Wildcard Dialog where you can define settings for bulk selection/deselection of the Action box of the items listed on page Select Items.
	Refresh Necessitated Items Explanation: Some objects are related together (e.g. entity and domain, entity and relationship). Let's say you uncheck a Domain in Select Object Types dialog. However you keep an Attribute of the Domain type checked for conversion. In the next screen the Domain will be selected for conversion (and highlighted in gray), even if you don't want it to. This is because of its relationship with the Attribute, which cannot exist without the Domain. Now, if you uncheck the Attribute, the Domain will still be checked for conversion. This is where you use this button. It runs through all checked objects and removes the Domain highlighted in gray since the Attribute is no longer checked. That means the Domain is no longer necessary, since it has no relationships with currently checked objects and you unchecked it in Select Object Types dialog.
	Expand All.
	Collapse All.
	Display options for properties.