Dekho server components are implemented in Java, which provides the best deployment options.
GIS services are provided to Dekho by ArcGIS Server. They are invoked via SOAP over HTTP.
Dekho communicates with external databases using JDBC (Java Database Connectivity). Connections and the queries to run are configured using the Dekho Administration GUI.
All Dekho server functionality is exposed as documented web services. This allows third party applications to easily leverage any component of the functionality. The server components also have various "web service triggers" where an external web service can be called as part of the response to an event. An example is calling an external web service as part of a feature edit, to allow synchronization to take place.
All Dekho web services require a session id to be passed. A session is established by calling the createSession web method on the Session web service, which returns a session id. The createSession web method performs the authentication (anonymous, Dekho, LDAP, NTLM or Kerberos) that is configured for the web application, using the credentials passed in.
Dekho can use external web services for search queries and for detail queries.
In summary, Dekho uses web services internally, provides web services for external use, and can consume external web services.