http://servername:port/OrganizationName/sdk/list.aspx
where
ServerName: Name of the server with port number.
OrganizationName: Name of the organization.
The data dictionary lists out both system and custom entities and attributes defined for the organization.
If you click on the icon in the Definition column, you can view all the attributes in the selected entity. At the top you can view ownership type of the entity, its type code, whether it is customizable, and if it is valid for Advanced Find.
In the next table we can see each attribute with various information as attribute type, length, valid for create, read, update and so on.
Also we can see the relationships of the current entity. It give a look of relationship name, condition, relationship type etc.
