The User Interface

This chapter describes the basic mechanisms and features of the web user interface generated by ERW. It is not an end-user manual.

As we mentioned before, ERW lets you edit instances of an entity-relationship schema. That is, it lets you create and delete entities and relationships, and change their attributes.

Each entity has an associated form, from which the user can modify its attributes and incident relationships. To access the form, the user must select the entity from the main list: it is a list of all existing entities. This list can be filtered in several ways, and is generated by the script list.php.

Once the user selects an entity for editing, a new window is opened that contains HTML input controls for attributes (text inputs, text areas, radio buttons etc.) and a number of complex structures for editing relationships. The content of the window is generated by the script form.php.

The rationale behind the editing of relationships is that you have a white-background list, containing the current relationships; and, immediately below, a grey-background list of entities that could be used to create new ones. Suitable buttons allow the user to perform relationship editing. For convenience, buttons that allow to create new entities or modifying existing ones are also allowed, but they can be inhibited.

Editing relationship attributes is also fairly easy: there is a set of input controls under the list of relationships. All new relationships get the attributes currently displayed. Moreover, whenever the user clicks on an existing relationship, its attributes are loaded into the controls (in this way it is easy to copy the attributes of an existing relationship). If the user wants to modify the attributes of an existing relationship, he or she has just to click on the relationship, modify the controls and click on the "Apply" button, which will apply the current values.

You can help the user to understand what's going on my making good use of the help attribute for attr and leg elements.

By default, ERW displays first all attributes, then filesets, and then relationships. Attributes are listed in the same order as in the ERL file; they are prefixed with their label, and the label is embedded in a STRONG HTML element if the attribute is mandatory. Of course, this can be changed using custom forms.

If an attribute cannot be modified, because it is read only, it is displayed in a different manner: HTML input control get their READONLY attribute set, whereas lists just display the available elements (e.g., relationships) on a grey background.

Often browsers do not support the READONLY attribute on sophisticated controls, such as drop-down lists. Of course, ERW will just discard any changes, but the user may not be aware of this fact.

Finally, the user can select among four buttons (any of which can be inhibited) to finish editing. "OK", as expected, save changes and closes the form. "Save" commits changes, but leaves the form open for further editing. "Save & Clone" commits changes, and creates a clone of the current entity that can be further edited and saved (this is most useful when doing repetitive data entry). Finally, "Cancel" will forget all changes.

You can tweak the default.php script, which generates the CSS style sheet, to change some details. In particular, DIV elements of class listborder surround lists: by choosing, for instance, the value scroll instead of hidden for the overflow CSS attribute you can display lists with scroll bars that let the user scroll to see long labels. Moreover, the editable attribute of the leg element allows you to select from which side the user can edit relationships.