Is there any established database schema to store references?
If you would consider an approach of storing bibliographic information in XML format, either directly (as XML files), or indirectly (via serialization or XML-to-RelationalDB conversion), you might find the following resources of interest (some of the resources are general and/or database-focused):


Metadata Object Description Schema (MODS) by The Library of Congress (USA);
Standards at The Library of Congress page lists a host of relevant information;
Apache OpenOffice bibliographic implementation and bibliographic database information;
development documentation for any other open source bibliography management software (JabRef, Zotero, etc.); for more information, see this list;
Dublin Core Metadata Initiative (DCMI);
List of citation standards, which might be used to store bibliographic metadata (by DCMI);
Finally, for the NoSQL way of doing things, consider using BibJSON schema and, for the linked data emphasis, consider using JSON-LD (also see this relevant article).