diff --git a/src/lib/cc/cpp/data_def.h b/src/lib/cc/cpp/data_def.h
index 95b8cd59e7..e5a28f8039 100644
--- a/src/lib/cc/cpp/data_def.h
+++ b/src/lib/cc/cpp/data_def.h
@@ -7,6 +7,12 @@
 
 namespace isc { namespace data {
 
+    ///
+    /// A standard DataDefinition exception that is thrown when a
+    /// .spec file could not be parsed.
+    ///
+    /// TODO: use jinmei's exception class as a base and not c_str in
+    /// what() there
     class DataDefinitionError : public std::exception {
     public:
         DataDefinitionError(std::string m = "Data definition is invalid") : msg(m) {}
@@ -16,9 +22,19 @@ namespace isc { namespace data {
         std::string msg;
     };
 
+    ///
+    /// The \c DataDefinition class holds a data specification.
+    /// Each module should have a .spec file containing the specification
+    /// for configuration and commands for that module.
+    /// This class holds that specification, and provides a function to
+    /// validate a set of data, to see whether it conforms to the given
+    /// specification
     class DataDefinition {
     public:
         explicit DataDefinition() {};
+        /// Create a \c DataDefinition instance with the given data as
+        /// the specification
+        /// \param e The Element containing the data specification
         explicit DataDefinition(ElementPtr e) : definition(e) {};
         // todo: make check default false, or leave out option completely and always check?
         explicit DataDefinition(std::istream& in, const bool check = true)