Lists

After having looked at Enif's graphic capabilities to produce network plots and diagrams, it should not be forgotten that often text-only type output is just as important for doing the day-to-day work in transportation planning.

This aspect is covered in Enif's concept of network lists. A network list is a user configurable object which displays textual and numerical information in tabular form for a set of network elements. Its implementation relies on the same basic concepts that were already discussed earlier: attributes, expressions, selectors, parameters and stylus. Using the ``Enif terminology'' which we have introduced in the previous sections, a network list can be described as an object consisting of the following components:

• Network element type: Defines the type of network elements that can be displayed by this list.
• Element selector: Defines the subset of network elements to be included in the list and, using the optional iterator expression, the order in which the selected elements appear in the list.
• Column attribute list: An attribute list containing one attribute for each column of the list. Each of these attributes is either pointing directly to one of the existing network attributes or is defined by a column expression to be evaluated ``on-the-fly'' when a list value is to be displayed.
• Column formatting information: Besides the usual formatting (field width, decimal precision, alignment), the value field can optionally be delimited by top, bottom, left and/or right rules, and for each column the pertinent summary information (min, max, sum, average) can be specified.
• Indexed stylus: Defines the visual appearance of each value field in the list. The stylus index is an expression of the corresponding network element type which is evaluated for each list value. The special constant attributes row and column can be used to make the stylus index depend on the row and/or column index of the displayed value field. Each list value is displayed using the resulting stylus properties by filling background, writing the value string and, finally, drawing the activated rules around the value field.
• List summaries: At the end of the list, optional minimum, maximum, sum and/or average summary rows display the requested column summary information.
• Other parameters: Similar as for plots, for each list configuration a name, a description, a window caption and an icon text can be specified.
• Optional ``by-element'' selector: A special variant of lists are the so called ``by element''-lists. These are lists which display a set of network elements which is determined by a related network element, such as e.g. ``O-D pairs by origin'', ``transit segments by line'' or ``turns by intersection''. In this case, an additional by-element selector specifies the subset and the order of the available by-elements. The current by-element can be chosen directly from the subset or stepped through consecutively in forward or backward direction.

The contents of a list can be sent to a printer or punched to a file. Network elements can be marked on the list and the marked elements can be temporarily hidden or copied to the clipboard for pasting into other applications.

Figure 27 shows an example of a screen shot of a list containing assignment results for the segments of a particular transit line. Note the use of the stylus to produce a ``zebra'' list background and to highlight the volumes of overcrowded segments.

Figure 27: Example of a list as it appears on screen