1. A method for assigning a new set of tags to a document, the method comprising: receiving, by a computer executing a document tag management application stored in a persistent storage of the computer, the document with a set of existing tags created by an author of the document via a network; receiving, by the computer using the document tag management application, a set of new tags created by a group of tag editors corresponding to the document via the network; processing, by the computer using the document tag management application, the set of existing tags created by the author of the document with the set of new tags created by the group of tag editors by: selecting, by the computer using the document tag management application, a new tag from the set of new tags created by the group of tag editors; analyzing, by the computer using the document tag management application, natural language semantics of the set of existing tags created by the author of the document and the selected new tag created by the group of tag editors using a tag subject matter ontology; calculating, by the computer using the document tag management application, a semantic distance between the set of existing tags created by the author of the document and the selected new tag created by the group of tag editors based on the analyzing of the natural language semantics of each tag using the tag subject matter ontology; determining, by the computer using the document tag management application, whether the calculated semantic distance between the set of existing tags and the selected new tag is greater than a semantic distance threshold value; and responsive to the computer determining that the calculated semantic distance between the set of existing tags and the selected new tag is greater than the semantic distance threshold value, calculating, by the computer using the document tag management application, a significance level for the selected new tag based on weighting factors, wherein the significance level for the selected new tag is equal to the calculated semantic distance multiplied by an application-defined adjustment value added to a tag weighting value given by the group of tag editors to the selected new tag multiplied by a reliability factor value corresponding to the group of tag editors; and assigning, by the computer using the document tag management application, the new set of tags to the document based on the processing of the set of existing tags created by the author of the document with the set of new tags created by the group of tag editors, wherein the computer using the document tag management application stores the new set of tags with the document.