LDAP (Lightweight Directory Access Protocol) directories are being widely used on the Web, for white pages information, user profiles, etc. The advantages LDAP offers are (ⅰ) the support for highly distributed data on the Web while still keeping a uniform data model; (ⅱ) the flexibility of a semi-structured data model, i.e. a flexible data type definition enabling the presentation and manipulation of heterogeneous data entries in a natural manner. Although many implementations of the LDAP protocol exist, the still lacking logical formalization prohibits a formal analysis and makes it difficult to make use of the numerous results developed for relational databases. In this paper, we give a first-order logic semantics of LDAP and discuss the expressive power of LDAP. In particular, schema typing constraints are interpreted as semantic integrity constraints. We apply our framework to the containment problem of LDAP queries with schema constraints; we reduce this problem to the containment problem of Datalog in the presence of integrity constraints.
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