RFC 1076 (rfc1076) - Page 2 of 42

HEMS monitoring and control language

RFC 1076          HEMS Monitoring and Control Language     November 1988


   This language is a component of the High-Level Entity Monitoring
   System (HEMS) described in RFC-1021 and RFC-1022.  Readers may wish
   to consult these RFCs when reading this memo.  RFC-1024 contains
   detailed assignments of numbers and structures used in this system.
   Portions of RFC-1024 that define query language structures are
   superceded by definitions in this memo.  This memo assumes a
   knowledge of the ISO data encoding standard, ASN.1.

   Distribution of this memo is unlimited.

INTRODUCTION

   This RFC specifies the design of a general-purpose, yet efficient,
   monitoring and control language for managing network entities.  The
   data in the entity is modeled as a hierarchy and specific items are
   named by giving the path from the root of the tree.  Most items are
   read-only, but some can be "set" in order to perform control
   operations.  Both requests and responses are represented using the
   ISO ASN.1 data encoding rules.

2. OVERVIEW AND SCOPE

   The basic model of monitoring and control used in this memo is that a
   query is sent to a monitored entity and the entity sends back a
   response.  The term query is used in the database sense -- it may
   request information, modify data, or both.  We will use gateway-
   oriented examples, but it should be understood that this query-
   response mechanism is applicable to any IP entity.

   In particular, there is no notion of an interactive "conversation" as
   in SMTP [RFC-821] or FTP [RFC-959].  A query is a complete request
   that stands on its own and elicits a complete response.

   In order to design the query language, we had to define a model for
   the data to be retrieved by the queries, which required some
   understanding of and assumptions to be made about the data.  We ended
   up with a fairly flexible data model, which places few limits on the
   type or size of the data.

   Wherever possible, we give motivations for the design decisions or
   assumptions that led to particular features or definitions.  Some of
   the important global considerations and assumptions are:

         - The query processor should place as little computational
           burden on the monitored entity as possible.

         - It should not be necessary for a monitored entity to store
           the complete query.  Nothing in the query language should



Trewitt & Partridge