The concept of the Entity is important within Sage CRM and is used through out the system.
When dealing with databases and designing applications the term entity can be used to describe anything of significance. This is true for both real and conceptual entities about which the system needs to hold information. An example of a concrete Entity is a Company, or a Person and a conceptual entity would be a Business Opportunity. Sage CRM doesn't make any distinction in the features it provides for either conceptual or concrete Entities. For example, when processing the data of a conceptual Opportunity entity a user will have very similar features available as when that user is finally able to record a concrete Order against the Opportunity.
If your background is in Database design then you are possibly more used to thinking of each entity in a system as generally corresponding to a physical table in the database. So you may well expect that the Order and OrderItems would be accessible as separate Entities within CRM. This is certainly the case. For design and customization purposes Sage CRM allows access to the physical tables as Entities. We can add additional columns to our Orders table and we can put table level scripts against the OrderItems. Each can be customized. We can see that the term Entity in Sage CRM can be used interchangeably with the words 'Database Table'.
The Entity Definition in Sage CRM is Contingent on Context within CRM
The term 'Entity' in Sage CRM is actually more complex. For example, a user who interacts with the details of a Company will be interacting with data drawn from not just the Company table but also the default address record associated with the company, the list of people and the phone and email information.
The term Entity can mean just the physically table but typically from a users perspective it means the larger scale business object that contains all information the user needs for the particular action they are carrying out within CRM. The Entity used in such user features as reviewing the Company Summary screen, using the internal email client from within an Opportunity Screen or seeing a reminder Notification display on the screen will draw its data from many tables.
In these cases the Entity has been defined by a view and that view will different in differing circumstances. This means that when we talk about the definition of an individual Entity in Sage CRM, thought must be given to the feature being used. The view used in the OpportunitySummary page may not be the same used in the MailMerge.
For example the different views that are used for mail merge are:
Primary versus Secondary Entities
In Sage CRM there is a division between Primary Entities and Secondary Entities. You see the primary entities listed within the main Administration>Customization screen. Primary Entities are also called Main Entities. The other entities are then accessed via the secondary entities drop down box. For example the Orders table in Sage CRM is presented as a Primary Entity, the OrderItems are presented as a Secondary Entity.
Below is a table that shows the main features that can be thought of as associated with a Primary Entity. The Entities that are Primary Entities in the default system are shown in blue.