| # Application Development The LN development environment enables you to develop LN software. You can create package VRCs in which you can perform the following: Set up a data model, consisting of domains and tables, for an application. To use this functionality, a development license is required. Create various types of software components, such as the following: Sessions Forms Reports Report scripts Multi-language data field labels Questions and messages Create, edit, and compile UI scripts, DLLs, and DALs. To use this functionality, a development license is required. Domains Domains define common information about data such as data type, length, alignment, valid ranges, display format, and capitalization rules. Table definitions A table definition defines the structure of a table. A table definition contains fields and indices. Table fields are linked to domains that define the data type and several characteristics of the fields. DAL The Data Access Layer (DAL) allows developers to describe rules about data. A DAL is linked to a table, not a session. Therefore, when the table is accessed, the DAL is used. In this way, different sessions can update a table by using the same rules. In addition, integration capabilities use the DAL to ensure updates are also processed with the same rules. Sessions A session performs an activity. Sessions are used to present data, edit data, and process data. Each session has a code. The session code is displayed in the status bar of the session window. A session consists of multiple components that work together, such as a form and an object. A session object is a compiled UI script. UI scripts The default behavior of a session is handled by the 4GL engine. If you require additional functionality or want to bypass the default functionality, you program your changes in the session's UI script (Program script). The UI script is compiled in the session object. The object contains only the exceptions to the normal operating procedures of the system. The 4GL Engine executes the normal operating procedures of the system, and you write the exceptions. Functions Functions allow you to perform a programming task multiple times with different values. A function is declared in the functions section of a script, in a library, or in a separate function script (include). Libraries A library, also called Dynamic Link Library (DLL), provides application-specific functions that can be used throughout the system, by many sessions. A library is a script that is stored in a separate component. The library is compiled independently of the program scripts that use it. Libraries are loaded at runtime by sessions that use them. When a session needs to access a library, the library is loaded, and the relevant routine is executed. See also Application Customization. |