A Package represents a Persistate application, or a major part of one. Persistate implements the industry standard MVC (Model View Controller) application architecture. In Persistate we use the term user interface in place of View, as the latter term is used in the 'database view' meaning. Consequently, a package contains a number of Modules, one Model, one Controller, and one or more UserInterfaces. In addition there is a StartUp Module, which is used to launch the application when it is run in stand-alone mode.

When you create a Package using the Persistate add-in, Persistate will create a solution in the IDE for you, and within that, one project for each module. This means that each Module corresponds to a .Net assembly - all of them DLLs, except for the StartUp Module which will be an executable.

A package is primarily a container for the PersistentClasses that you define for your application. These can be ObjectClasses, DataClasses or ViewClasses. You define these classes by writing a definition file in the English like Persistate definition language. You then user the Persistate add-in to create the C# classes which implement the defined Persistate classes in memory, as well as creating the necessary database objects to store instances of your classes in persistent storage.

As well as classes, you can define ClassCategories and Workspaces in your definition file. You probably won't need many or any of the former, as there are a good set of categories defined for you in the standard Persistate Package. However, you will usually define at least one Workspace if your application uses a user interface, as these describe the arrangement of the Panes in your application windows.

When you write your definition file you can import and use the classes from other Packages using the Use statement. Before you process your definition file you must add any thus named Packages into the UsedPackages collection. Normally you will do this using the Persistate add-in.

Packages are contained in a parent Environment object, and this is their development environment. They can be added to the UsedPackages collection of any number of other environments. In both cases, any singleton objects defined in the Package will become entry points in the Environment. In other words, the Environment will contain a persistent sub-tree as defined in the Package definition file.

Before you can store objects defined in a Package in persistent storage, you must first prepare one or more Databases by giving them the necessary database objects (tables, views, etc..). You normally do this using the Persistate add-in, but you can also use the AddTargetDatabase method, which does the necessary and adds the database to the TargetDatabases collection.