+<sect>Implementation
+
+<p>
+The implementation of the email server includes all the modules described
+in the design deliverable.
+
+The work was roughly carried out as follows:
+<enum>
+<item>The logging facilities and resource management utilities were
+ implemented — virtually all other modules depend on these
+ modules.
+<item>A minimal ES was implemented — including a high-level
+ API to the Z39.50 sub-system and a CCL parser with a few
+ commands, such as FIND and SHOW. This version displayed MARC
+ records in a raw format. This version served as base for the URP.
+<item>The first version of the MARC display formatting tool, FML,
+ was implemented and included in the ES.
+<item>The ETI program was implemented along with the IPC
+ (interprocess communication) utilities based on FIFOs. Facilities
+ to keep connections alive (to Z39.50 targets) was implemented.
+ To identify a user, a file-resident symbol table (small database) was
+ implemented which maps a email username to a unique integer (email userid).
+<item>The protocol persistency was implemented and more CCL commands
+ were added.
+<item>The MONITOR program was implemented.
+</enum>
+
+The following sections cover the most important modules in the ES and
+deviations from the design.
+
+<sect1>Z39.50 Interface layer
+
+<p>
+The design report specified that the Zdist toolkit from CNIDR would
+be used in the ES to provide access to the Z39.50 protocol. The package
+was choosen bacause it is easy to use and, more important, we felt
+that the API would be reasonably stable and supported.
+
+Nevertheless it turned out that CNIDR choose to change the API
+completely around January 1995 and announced a new version
+called zdist102b1-1.
+
+<em>Note: As of this date the newest version of Zdist is still
+zdist102b1-1. CNIDR seems to concentracte on their Isite package
+which also includes a Zdist package presumably similar to the
+standalone Zdist package</em>
+
+During the work with the Zdist package a few bugs were discovered.
+Fortunately, they could be solved within a few days. We also
+discovered that the package lacks result-set references.
+We posted the bug fixes to Kevin Gamiel who is responsible for
+the package but we didn't get responses. So, eventually, we weren't
+satisfied with the package after all.
+
+In February some of us began the development of a new Z39.50 package
+called YAZ — in retrospect somewhat motivated by the
+experiences with existing Z39.50/SR toolkits.
+
+To support result-set references we chose to incorporate a YAZ
+interface in the ES also. And we designed and implemented a
+simple high-level Z39.50 origin API that supported both Zdist and YAZ.
+
+The protocol persistency module was implemented on top of
+the high-level API and not on top of Zdist. The obvious
+advantage is that the persistency module is not tied to one
+particular Z39.50/SR package.
+
+Persistency information stored for each user is simply:
+<itemize>
+<item>hostname and port number.
+<item>authentication string
+<item>selected database(s)
+<item>next result set number
+<item>next result set position
+<item>result set information
+</itemize>
+
+Information about each result set includes:
+<itemize>
+<item>name
+<item>size (number of hits)
+<item>database(s)
+<item>query
+</itemize>
+
+<sect1>CCL
+
+<p>
+The CCL was implemented as described in the design. A CCL utility
+was made as a separate module which implements a tokenization
+package and a parser which translates from FIND to RPN. The
+data structure used to represent the RPN query is also used in
+Z39.50 search API on top of YAZ or Zdist.
+
+The CCL parser is quite configurable. Token names can be redefined to
+one or more names (aliases). Also, the specification of mapping
+between CCL field names (qualifiers) and Bib-1 attributes can be
+specified in either the C API or a file.
+
+Although the Z39.50 system in the ES uses the Bib-1 attribute set, the
+CCL parser itself is not tied to Bib-1.
+
+<sect1>FML
+
+<p>
+
+<sect1>IPC
+
+<p>
+