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Layered Topic Maps

Page history last edited by Dmitry Sokolov 5 years, 7 months ago

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Can be useful for Multi-Space Frameworks?

http://www.wandora.org/wiki/Introduction_to_Layered_Topic_Maps#Layered_topic_maps_in_Wandora

Layered topic maps in Wandora

Wandora uses a layered topic map paradigm. Topic maps are organized in layers, each layer containing one topic map. Each topic map can be turned visible or invisible. The topic map that the user sees is the merged topic map of all visible topic maps. However, internally Wandora does not perform a complete merge operation at any time so switching layer visibility is a relatively fast operation. Only the topics visible on the current page are merged. Because changing layer visibility is fast, the user can easily focus on one topic map or view the entire merged information.

The order of layers is used to decide which piece of information is visible when there are different values for some properties of topic. In the reduced topic maps that Wandora uses, topics can have only one base name, only one subject locator and only one occurrence for each scope. If two topics that will be merged have different values for one of these properties, we have to decide which of the possible values actually is used in the merged topic map. Value from the topmost layer is used, if there are several different values in topmost layer, one of them is chosen arbitrarily. Note that we wouldn't need to do this if Wandora used complete standard topic maps, because they may have several base names, subject locators and occurrences. We could simply have them all in the merged topic.

Each layer contains one topic map. You can use different topic map implementations in each layer. For example you can use a database stored topic map in one layer and memory implementation in another. It is also possible to use a layered topic map in a layer which makes it possible to organize layers in several layer groups. This will result in a tree structure where layered topic maps resemble folders in a file system.

At all times, one of the layers is selected. All edit operations in the topic map are done in this selected layer. This may cause implicit duplication of topics when the visible topic is not in the selected layer. This is discussed in more detail below. If you use layered topic maps in layers, choice of selected layer is slightly more complicated. All edit operations are always done in a leaf layer, that is a layer that is not a layered topic map. Hence if you select a layered topic map layer, all edit operations will actually be done in some child layer of the selected layer. This layer will be the last selected layer under the layered topic map and it is highlighted in the GUI with a slightly lighter colour than the selected layer.

Note that the layers in Wandora resemble the layers paradigm used in many image manipulation programs. Just like in Wandora, these programs allow user to switch layer visibility and all edit operations are done in the layer user has selected. Also topmost layers overwrite information from bottom layers by drawing over them.

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