In this section we discuss the data types available in MetaEdit+ and how they appear to users in property dialogs. To set the data type for a property, use the Datatype pull-down list in the Property Tool. If you select a metatype (Graph..., Object..., Port..., Relationship... or Role...) a dialog will prompt for selection of a particular type of that metatype.

The string data type is an ordinary character string without any formatting. The initial default value is empty.

The Widget pull-down list (Figure 2–18) is used to select among a list of possible widgets used in property dialogs for entering a string value: Input Field, External Element, Editable List, Overridable List, Fixed List, SOAP Fixed List and Radio Button Set.

The default selection is Input Field, which is a single line box of approximately 30 characters by default (it can be resized). The External Element widget type is used when the string represents a file, resource or command in the operating system. The widget used is identical to that for a normal Input Field, but its menu has an extra Execute item, which sends the contents of the property as a string to be run by the operating system. For example, in Windows this can be a text file, a Word document, a URL (e.g. http://www.metacase.com, or mailto:info@metacase.com), or a command. The menu also has a Browse... item, to allow easy selection of a new filename as the value.

The next four widgets all use pull-down lists, whose initial set of values is defined in the property type. In a Fixed List the user can only select among the predefined values. The SOAP Fixed List is a special case of a Fixed List, where the list values are retrieved from an external source using SOAP calls. This requires the configuration of the SOAP server connection and retrieval message. When the SOAP Fixed List widget is selected, the Property Tool appears as in Figure 2–19. Select the SOAP server and method from the pull-down lists.

To define a new SOAP server, press the Edit button next to the SOAP Server pull-down list. This will open a dialog for SOAP server configuration (Figure 2–20). To define a new SOAP server, enter its name and URLs for the WSDL file and the actual server (e.g. file:///c:/myservices.wsdl and http://localhost/myservice). To finalize the creation of the SOAP server definition, press the Add button. The SOAP server now appears in the list on the left. To edit an existing SOAP server definition, select it from the list, edit its values on the right pane and press the Modify button to confirm the changes. It is also possible to view those property types using a SOAP server definition by selecting it from the list and pressing the Info button. To remove a SOAP server definition, select it from the list and press the Remove button (remove is not allowed if there are still property types associated with the selected SOAP server definition).

In an Overridable List the user can type a different value from those in the list. In an Editable List new values of the property that are typed in the field will be added into the list. Note that the Editable List’s list contents are based on the values entered into the value list by metamodeler, but each project that uses this property type uses its own copy of the list, and the new items that the modelers add will only appear within that project. Use the Reset Projects button next to the value list to reset these per-project copied lists of Editable List values.

For the list types a Value list appears below the widget list. The Value list contains the predefined values for this type. The list pop-up menu allows addition, removal and changing the order of the values. Note that for Editable Lists, this value list is often empty: the contents of the list are built up separately for each project. The value list can also be edited conveniently in a text editor, one value per line, by choosing Edit as Text from its pop-up menu.

A Radio Button Set is a special case of a list widget. The initial values are given in the Value list like other list-based widgets, but they are presented as radio buttons in the property dialog.

Text is used for longer descriptions. The text can contain carriage returns, tabs etc., and also basic text formatting (fonts, bold, italic etc.). The text widget is shown as a multi-line text box with a vertical scroll bar. Text properties can also be opened in a Text Editor, useful for text formatting or longer texts.

Number can contain any integer, scientific or real number. The widget for number is a single line box with initial value 0.

Normally, it is better to use a String, since although a property may initially appear to only contain numbers, it may later be found useful to allow some strings too, e.g. to represent common constants. Input can be restricted with the Value Regex field.

A Boolean data type holds the value true or false. The widget for Boolean value is a check box: the initial value is false.

A creation timestamp stores the element creation time. The value is stored as a UTC timestamp, and offset by the local timezone when displaying. Its value cannot be changed, thus the widget for timestamp is a read-only input field.

The Collection data type defines a list of strings or objects, initially empty, in which the user can add and delete items. The widget for Collection is a list box with a vertical scroll bar.

An example of a collection can be found from the Watch example in type Display, which includes collections of Icons, UnitZones and Buttons. Each of these has properties of their own and these properties could again be collections themselves. MetaEdit+ does not limit the number of such levels of complex properties.

Selecting the Collection data type adds an Item type pull-down list to the Property Tool window, showing the data type of the members of this list. The list members can be strings, graphs, objects, ports, roles or relationships. If you select a metatype (i.e. anything other than String) a dialog will prompt for selection of a particular type of that metatype. That type will then be shown in the Item type field.

When a type is chosen the list members can always be not only of the type specified in the Item type field, but also of any type which inherits from that type. In some exceptional circumstances it may be desirable to specify the supertype of all the types of that metatype, e.g. Object: you can do this by selecting the metatype from the Item type pull-down list with shift held down, and that metatype will then be included in the list of types to select from.

An individual graph, object, relationship or role can also be used as the value of a property. In this section we discuss object types, but the same applies for the other non-property types as well.

The Object data type allows you to specify a property whose content will be an object of a selected type. When you select this data type, the tool further asks you to specify the object type, which is the type of the objects that can be attached to this field. Again, instances of subtypes of this type are also allowed as values for this kind of property. In some exceptional circumstances it may be desirable to specify the supertype of all the types of that metatype, e.g. Object: you can do this by selecting the metatype from the pull-down list with shift held down, and that metatype will then be included in the list of types to select from.

The widget for the Object data type is similar to a String property’s Input Field, except that the background is gray, showing that you cannot type directly there. The box shows the identifier of the currently attached object. In place of the normal text editing operations in the pop-up menu, there are operations for editing the attached object, or opening its representation.

This data type — containing other non-property instances — is a very powerful tool for several purposes. It can be used for attaching whole objects or graphs into one property of another object or graph type and thus allowing complex data structures.