The VACOS project aims to provide better support for searchers with

vague information needs formulated in natural language. We consider two

use cases: product search and research data search. In the first phase

of the project, our human-centered development process focused on

analyzing the user context, creating datasets with natural language

information needs, enriching datasets with topical and natural language

attributes, and developing prototypes for object search. The results of

the first project phase have shown the necessity to searchers not only

during the initial search process but also to explain search results and

their relation to the formulated search request. Therefore, concepts of

the research areas "Conversational Search" and "Explainable Search"

will be used in the second project phase. First, object metadata will be

enriched to generate object representations that better match

information needs formulated in natural language. Based on this,

mixed-initiative natural language search dialogues will be developed.

For the presentation of search results, various representation forms

will be investigated, focusing on vagueness and explainability. Single

result items will be explained with respect to the formulated search

request as well as in comparison to other found objects. In the context

of this proposed project, the prototypes developed in the first project

phase will be extended by new dialog and explanation components.

Human-centered evaluations will be conducted to examine natural language

and conversational supports for object search.