Glossary

This document defines the common nomenclature used within mKTL. Some of the terms are inherited from KTL; some are inherited from common design patterns in the broader software world. Where there is a conflict between the two, we prefer to use the common industry definition rather than traditional use within WMKO.

External definitions

• WMKO:

  W. M. Keck Observatory, where mKTL was initially established, in collaboration with WMKO partner institutions at the University of California and California Institute of Technology.

• KTL:

  Keck Task Library, the predecessor to mKTL at WMKO. KTL is a key-value application programming interface (API), written in C, and has been the dominant API for interprocess communication at both WMKO and Lick Observatory since the 1990’s.

• EPICS:

  Experimental Physics and Industrial Control System, another key-value API that WMKO adopted for its telescope and adaptive optics control systems. EPICS is one of the interprocess communication APIs for which KTL provides a common abstraction.

mKTL-specific terms

• mKTL:

  Modern Keck Task Library. It’s just a name, but it’s ours, and was the clear choice out of a field of a dozen options that were presented to the future power users of the protocol.

• Protocol:

  Protocol, as used in the above statement, refers to a communication protocol, as opposed to being a synonym for an interface in an object-oriented context. Borrowing phrasing from Wikipedia, a communication protocol defines the rules, syntax, semantics, and synchronization of communication between two entities.

• Transport:

  A transport layer is the underlying layer of the network stack that handles application level messaging. Though it is built upon TCP and UDP, ZeroMQ is effectively the transport layer for the mKTL protocol.

• Daemon:

  A persistent process responsible for some or all of the key-value pairs in a given store. When client requests are initiated it is the daemon that will be contacted to satisfy the request. This is analogous to a KTL dispatcher or an EPICS IOC.

• Store:

  A store is an aggregation of individual key-value pairs. Within a given deployment of mKTL the store will have a unique name. This is analogous to a KTL service, or an EPICS database, and is effectively an associative array, or a Python dictionary. “Database” is another term used in similar contexts, but that term is more commonly used in reference to a relational database. mKTL treats the store name as case-insensitive, any actual usage will render it as all lower-case.

• Key:

  A unique name within a store, identifying a single key-value pair. This is analogous to a KTL keyword, or an EPICS channel. mKTL treats the key as case-insensitive, any actual usage will render it as all upper-case.

• Value:

  The other half of the key-value pair. Like a KTL keyword, a mKTL value can be one of many native types (integer, floating point, string, etc.), and includes the possibility of compound values, similar to KTL arrays.

• Item:

  The combination of the key/value pair. This term is borrowed from Python’s dictionary, where it has a similar meaning. In the context of mKTL, the Store class in the reference Python module will return Item instances when referenced by the key.

• Get:

  Retrieve a value corresponding to an individual key in a store. A typical client can issue a blocking or a non-blocking (synchronous or asynchronous) operation. This is analogous to a KTL read or an EPICS get.

• Set:

  Establish a new value for an individual key in a store. A typical client can request a blocking or a non-blocking (synchronous or asynchronous) operation. This is analogous to a KTL modify or an EPICS put.

• Publish:

  Broadcast a new value for an individual key in a store. The store name combined with the key makes up the bulk of the topic, which in turn has specific meaning in a typical publish-subscribe design pattern.

• Subscribe:

  Request the receipt of any/all published broadcasts of an individual key in a store. This is analogous to a KTL monitor or EPICS monitor request.

• Callback:

  A method to be called whenever a published broadcast arrives for an individual key in a store.

• Register:

  The act of associating a callback with a specific key in a store. The callback will now be invoked whenever the value of that key changes. “Connect” is another term used in similar contexts, but that term is more commonly used with network sockets.