9 Scheduling module

9.1 Scheduling concepts and definitions

There can be no concept of "alignment" or "synchronization" (which is alignment in time) of objects without the more basic concept of "scheduling" them; that is, giving them a position and size. Scheduling, in turn, requires a set of coordinate axes and a system for measuring on them, collectively called a "coordinate space". In HyTime, a coordinate space has a finite extent along each axis and is known as a "finite coordinate space" (FCS).

NOTE 254 An FCS is also a "finite coordinate space" in the mathematical sense that it has a finite number of axes or dimensions. In mathematical terminology it is also a discrete coordinate space because each axis has a finite number of points.

An object has no inherent extent or position in a coordinate space. It is given them by incorporating the object in an "event", which is positioned in a list of events, called an "event schedule". A coordinate space can have many event schedules, each of which is aligned with the coordinate axes.

The positioning of an event in a schedule is one of the values specified by the event's "scheduled extent". A scheduled extent consists of dimension specifications, one for each of the axes of the coordinate space, which collectively define both the position and the literal extent of the event.

Within an event schedule, logical groups of events can be combined into an "event group" in order to associate common properties with them.

In HyTime, each axis of a coordinate space is assigned to a measurement domain that is based on a standard measurement unit (SMU), such as the Systeme International second, or the Systeme International meter. An application can also define virtual measurement units that have no physical basis (that is, are not "real"). These are figures of merit that can represent relative extents. During rendition (see 10 Rendition module) of the document, virtual measures can be projected onto any real measurement domain that is appropriate, or onto another virtual domain.

NOTE 255 For example, at rendition time a virtual unit could be assigned a fixed value, an algorithmically generated variable value, or, in the time domain, be related to a click track recorded by a performer.

NOTE 256 If convenient, a virtual unit could be thought of as corresponding to a unit of real measurement. Such a convention would not preclude the creation of other renditions made according to other methods.

NOTE 257 Axes need not be temporal or spatial; the quanta can denominate any measurable thing, for example money, temperature, and mass, making the FCS concept broadly applicable to the visualization of information. Some applications may even use an axis to impose an arbitrary order on some set of topics, one quantum per topic, as seen in certain kinds of tabular information. In the latter case, depending on the topics themselves and the significance of the order thus imposed, it may or may not be meaningful to say that (topic one) + 2 = (topic three).

			Copyright © 1992, 1997 International Organization for Standardization. All rights reserved. This electronic document is for use during development and review of International Standards. Official printed copies of International Standards can be purchased from the ISO and the national standards organization of your country.
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