Reduced Topic Maps
Wandora uses a slightly reduced version of Topic Maps. This improves the performance of Wandora and the parts of the standard topic maps which are not usable directly, can usually be still expressed in the topic map in some other way.
Most notable differences are
- Subject identifiers and subject locators are never resolved. This means that they are simply used as identifiers and it has no effect at all whether or not the URI refers to an actual local or online document.
- Only one base name is allowed per topic and base names cannot have scopes.
- Variant names are not base name dependent but are all considered to be variants of the single base name of the topic. Variant names can have scopes.
- No resource reference occurrences, only resource data. When a reference occurrence would be needed, it can be expressed by creating a new topic for the referred URI, using the URI as the subject locator of the new topic and then association the two topics.
- Occurrences can only have a scope of one topic. This is usually used to store the language of the occurrence.
- Topic can contain only one occurrence per type and scope.
- Topic can contain only one variant name per scope.
- Associations cannot have scopes.
- Associations can only have one player per member and cannot have two members with same role.
- No reifiers. Thus, an explicit reifier can not be added to a topic, an association nor any other topic map structure. When a topic or an association needs a reifier, it can be implemented using an association or an association player.
It should be noted that many of the features that were left out are somewhat vaguely defined in the topic map standard. For example, the interpretation of scopes is almost entirely left to the application, as is the decision when to resolve subject identifier URIs.
The reduced topic maps that Wandora use are still valid standard topic maps and can be used in other applications than Wandora. When importing topic maps from other applications, some information may be lost due to these restrictions.
- Although topic map implementation does not resolve subject locators, Wandora application views an icon or a thumbnail for the subject locator and the icon is created using the subject locator resource. To create the icon or a thumbnail, Wandora must resolve the subject locator and download the image.
- As Wandora doesn't resolve identifiers, you may use invalid URI as a subject locator and a subject identifier. Exporting a topic map containing invalid URIs in RDF format, for example, results an invalid RDF serialization.
- Base and variant names in Wandora should not contain new line characters as the GUI element holding a name supports only single line strings.