Since 1999, I've been editing the Database Principles Column of SIGMOD Record which publishes surveys of recent results that appear in database theory publications (such as ACM PODS or ICDT) in a form suitable for the larger audience of the Record.

Some of the best database theoreticians (and not only database theoreticians) contributed  papers on many different aspects of databases. All of them can be found here.

Serge Abiteboul
   On views and XML (pdf)

Guozhu Dong, Juanwen Su
    Incremental Maintenance of Recursive Views Using Relational Calculus/SQL (ps)

Jan Van den Bussche
    Constraint Databases: A Tutorial Introduction (pdf)

Alon Halevy
    Theory of Answering Queries Using Views (pdf) 

Peter Buneman, Wenfei Fan, Jerome Simeon, Scott Weinstein
    Constraints for Semi-structured Data and XML (ps)

Luca Cardelli
    Describing Semistructured Data (pdf)

Dan Suciu
    The XML Typechecking Problem (pdf)

Ronald Fagin
    Combining Fuzzy Information: an Overview (ps)

Frank Neven
    Automata theory for XML researchers (pdf)

Martin Grohe
    Parameterized Complexity for the Database Theorist (pdf)

Victor Vianu
    From Codd to XML (ps)

Diego Calvanese, Giuseppe De Giacomo, Maurizio Lenzerini, Moshe Vardi
    Regular path queries (pdf)

Thomas Schwentick
    XPath Query Containment (pdf)

Georg Gottlob, Christoph Koch
    Logic-based Web Information Extraction (pdf)

Sara Cohen
     Containment of Aggregate Queries (pdf)

Rick Hull, Jianwen Su
     Tools for Composite Web Services: A Short Overview (pdf)

Francesco Scarcello
     Query Answering Exploiting Structural Properties (pdf)

Alin Deutsch, Lucian Popa, Val Tannen
     Query Reformulation with Constraints (pdf)

Leopoldo Bertossi
     Consistent Query Answering in Databases (pdf)


Phokion Kolaitis and friends on data exchange

Marcelo Arenas on XML normalization

Luc Segoufin on logics for trees with data values