This repository features an extension of the java.util.Map<K, Set<T>> interface for supporting subset and superset queries over sets of tags associated with keys. Most prominently, an implementation based on the Set Trie datastructure is provided, which is an Index Data Structure for Fast Subset and Superset Queries based on the paper by Iztok Savnik.

The artifact is published on Maven Central, and thus ready for use in your project.

<dependency>
    <groupId>org.aksw.commons</groupId>
    <artifactId>tagmap-core</artifactId>
    <version>1.0.0</version>
</dependency>

The project introduces the TagMap interface with the following important properties:

• At the core it is a Map which associates keys with sets of "tags".
• It enhances the Map with methods for retrieving keys by subsets and supersets of tags.

public interface TagMap<K, V>
    extends Map<K, Set<V>>
{
    TagMap<K, V> getAllSubsetsOf(Collection<?> set);
    TagMap<K, V> getAllSupersetsOf(Collection<?> set);
}

NOTE: The interface supports iterative refinement of a TagMap, however, at present, all implementations return a TagMapSimple which has linear complexity

The following implementations exist:

• TagMapSimple: A basic implementation which is backed by a standard Map and implements the sub-/superset queries by means of sequential scans
• TagMapInvertedIndex: An implementation which internally tracks for every tag the set of keys it is associated with.
• TagMapSetTrie: An implementation of the Set Trie datastructure proposed by Iztok Savnik.
• For validation, we provide a util function in ValidationUtils which creates a Java proxy which delegates each method invocation to two implementations, compares the return values for equality, and raises an exception if they differ.

TagMap<String, Integer> simpleFm = new TagMapSimple<>();
TagMap<String, Integer> setTrieFm = new TagMapSetTrie<>();
TagMap<String, Integer> invertedListFm = new TagMapInvertedIndex<>();

TagMap<String, Integer> fm = ValidationUtils.createValidatingProxy(setTrieFm, simpleFm);

fm.put("a", Sets.newHashSet(1, 2, 3));
fm.put("b", Sets.newHashSet(1, 2, 4));
fm.put("c", Sets.newHashSet(2, 3, 4));



fm.getAllSubsetsOf(Arrays.asList(1, 2, 3))
    .entrySet().forEach(e -> System.out.println("" + e));


fm.getAllSupersetsOf(Arrays.asList(1, 4))
    .entrySet().forEach(e -> System.out.println("" + e));