# Defining fields

An important part of defining a module is defining the fields belonging to it. In the screen you see two tables, one with the predefined fields (from the selected module type) and one with the newly defined fields. The predefined fields cannot be changed or removed. You can however create, alter and remove fields from the New Field section (lower part of the screen).

- | Remove Field Removes the selected field from the New Field section.
- | Add Field Opens the Define Field dialog to create a new field.
- | Change Field Can be used to alter an existing field. When altering existing modules changes you can make here are limited. In any case most changes can be achieved by using the settings, such as the General Field Settings.

## Creating a field

To create a new field press the "add field" button. The following dialog will open:

### Name

The name of the field as displayed on screen. For existing modules the name can be overruled by setting a label in the General Field Settings.

### Can be searched?

Indicates if users can search / filter on this field.

### Required

You can mark a field as a required field. This field must always be filled when saving. The item will only be saved when all the required fields have been filled. For existing modules change this using the General Field Settings.

### Descriptive?

When a field is marked as descriptive (or a combination of several fields) the value of this field is used to represent the items. For existing modules change this using the General Field Settings.

### Is key field

The combination of the key fields will be used to check if the item already exists (more about this). For existing modules change this using the General Field Settings.

### Item form tab

Defines the tab of the item form where the field will be placed. For existing modules change this using the Item Form Settings.

### Maximum field length

The maximum input length for this field (in characters).

### Field type

There is a wide range of field types available and most of them speak for themselves. However the single reference and multiple reference fields need some more explanation. When you select either of these field types you will notice the reference module list becoming active. With these field types you can create a reference to another module. If you select a single reference field Data Crow will create a list of items from the selected module (such as is the case with categories for software). Only one of these items can be selected. If you select a multiple reference field the field can hold more than one property items (such as with the genres for Music Albums). A field with an item select dialog is created.
Another note on reference fields; when you make a reference to a property module the items of this module can be managed from the "tools" menu. A reference to any other type of module will make of the referenced module a sub-module of the current module. Such is the case for example with actors for the movie module. The actor module is referenced by the movie module, making the actor module a sub-module of the movie module. The sub-module is displayed in the module bar when you select the referencing module.

### Reference Module

Used for reference fields only. See above for further explanation.