Lexicon

From Picswiki

PICS Terminology

This documentation uses specific meanings for some words and terms that have additional meanings elsewhere. Hopefully, the definitions provided here will help clarify the meanings used throughout the PICS documentation.

ACC

a.k.a. PICS Access Control Client

This is the program that users outside the dedicated PICS network use to access PICS data. ACC provides the ability to log on to PICS (possibly to any one of several PICS, if so configured) and after logging in, shows the PICS programs that may be started/stopped (and their current status).

Agent

The provider of a service interface in a node. The actual program providing the interface could be different in each node, but its interface will be the same. As an example, SDB and SdClient are Static agents. Currently there are only Realtime and Static agents.

backup

The node is a subsystem that is passively waiting for the primary to fail (or otherwise go away) so that it can assume the primary role. Many backup tasks perform all of the actions of the primary, with the exception of anything that leaves the machine (i.e. archivers record data, but don't serve it; compute tasks perform the appropriate calculations, but do not share the results; etc.).

DARS

a.k.a. Data Archive and Retrieval Service

Stores periodic snapshots of all real time data values at several resolutions. The snapshot records are kept in circular files, allowing only a limited historical time window at each resolution. As the distance back in time increases, the resolution available decreases. This data is normally used only back-filling graphic plots of data.

DEU

USEC/PGDP term for PICS display nodes. This term originally described the control room devices that allowed the operators to monitor a single value on a vacuum-fluorescent display via a serial link to the MODCOMP unit computer and was used as the name of an application that mimicked the devices. Although the term is utterly obsolete, PGDP personnel have taken to calling the PICS display nodes "DEU's."

node

A single computer within PICS. This is used to differentiate between a subsystem, which may be one or two nodes, and the computers that make up a subsystem.

OPAL

Operator Programmable ALarm application

PDRS

a.k.a. Plant Data Recorder Service

Stores [almost] the entire real time data stream in a series of hourly data files. Each data file begins with a snapshot of the entire database at the time the file was opened, followed by all significant change records that occur until the end of the hour (when the next file is started). PDRS uses its own set of refresh and significant change settings to determine home much data to write into the archive files. By default, those values are set the same as the refresh and sig change threshold for the original data provider (making PDRS record everything).

peer

A node in a subsystem that does not offer any services or data to other machines. Peer nodes are generally only consumers of data from PICS. The sole exception is that peer nodes may run applications that make changes to the static database.

PICS

a.k.a. Plant Integrated Computer System

PICS date

Stored as an unsigned 16 bit integer, PICS maintains the date as the number of days since Jan 1, 1980. In this system, Jan 1, 1980 has a value of zero and Jan 1, 1981 has a value of 366, etc.

PICS time

Stored as an unsigned 32 bit integer as the millisecond in the day.

PICS time tag.

PICS time tag

The combination of a PICS date and PICS time stored in memory in that order.

point

In data acquisition systems a point refers to a unit of collectible data. The data can come from front-end gear from an analog or digital sensor; can be derived from other points; represent the state of a subsystem; etc.

primary

The node in a subsystem that is actively performing the subsystem's duties (like providing data, managing a database, controlling hardware, etc.).

RTDB

a.k.a. Real Time DataBase

All of the scanned and computed data point values and their quality/status is stored in the RTDB.

Every node maintains a complete copy of this database, and all nodes running a primary data provider application broadcast new values so that all other nodes on the network (including themselves) can receive the new data.

RTDBA is the primary RTDB agent within the dedicated PICS network, and RTClient is the typical agent outside the network.

SDB

a.k.a. Static DataBase

This contains the descriptions, alarms and control settings for all of the real time data points in PICS. The name derives from the fact that this data is relatively unchanging (i.e. 'static') ... at least compared to the real time data.

There is a single master static database (primary and backup) within PICS. Each node maintains a cached copy of much of the data, organized for quick and easy access by applications.

SDB is the primary agent (i.e. actually managing the physical database) and runs on only ONE subsystem in PICS. All other subsystems use SDClient as their SDB agent.

section

A designated subset of the subsystems in system. A section must contain a master subsystem. Typically a section will embody most of the elements of a whole PICS that are in a localized physical area such as one building.

side

When a subsystem contains two computers, one is considered the 'A' side and the other is the 'B' side. (Actually, even when only one machine is in a subsystem, it still has a side and may be either 'A' or 'B'.)

subsystem

One or two computers that share a name (except for side) and often share a set of tasks.