Historians, IIoT & Industrial Data Glossary
Process historians, time-series data, IIoT and edge computing, integration patterns, and industrial data management. 141 terms in this topic - each defined in plain English on its own page.
Once a value is measured it has to be stored, moved, and made useful - that is this topic. It spans process historians and time-series storage (compression, retention, backfill), the integration patterns that move industrial data between systems (APIs, buses, edge gateways), and the IIoT and analytics vocabulary built on top of that data. If SCADA is the live view, this is the memory and the plumbing behind it.
141 Terms
What Is an Aggregation Function in a Time-Series Query?
The family of avg, min, max, count, and sum that collapses many samples into one, and which answers which question.
Read → GlossaryHistorian & Data / Storage / Archive Partitions
Time-bounded archive chunks for retention, backup, and query pruning, and what happens at an archive shift.
Read → GlossaryHow do you backfill a historian from a CSV file?
Map timestamp, value, and quality columns, handle timezone and duplicates, tag as substituted, then verify against archive rules.
Read → GlossaryBad quality flags across a whole site: what causes it?
Read the quality state and scope, then split a comms timeout from a device fault from a config change.
Read → GlossaryWhat Is Boxcar & Backslope Compression?
The older two-test compression that predates swinging door, and why it leaves stepped, jagged trend artifacts.
Read → GlossaryBuild a Master Alarm Database
Structure one row per alarm with identity, configuration, rationalized knowledge, and source links, then put it under change control.
Read → GlossaryHistorian & Data / Tags / Calculated Tags
Derived historian points computed from other tags, and the recomputation problem when their source data is backfilled.
Read → GlossaryWhat Are Calculated Tags (Derived Points)?
SCADA points whose value is computed from other tags via sums, differences, and unit math.
Read → GlossaryWhat Is a Canonical Data Model?
One common intermediate format that ends N-squared point-to-point mappings and gives multi-vendor operators a single schema.
Read → GlossaryEdge or cloud historian?
Decide by outage behavior and query scope: buffer at the edge so nothing is lost, keep the system of record central for fleet-wide queries and long retention.
Read → GlossaryWhat Is a Cold-Archive Storage Class and How Does Retrieval Latency Affect Historian Design?
Cheap deep object-storage tiers with minutes-to-hours retrieval, and how that latency shapes what stays cold.
Read → GlossaryHow do you tune a compression deviation limit?
Set a per-tag deviation limit from instrument noise and required fidelity, then validate against raw data and reconstruction error.
Read → GlossaryWhat is compression reconstruction error?
Largest gap between the historian's interpolated line and the real signal, bounding the worst-case error in any compressed value.
Read → GlossaryWhat Is a Data Quality Confidence Score in SCADA?
Rolling completeness, staleness, violations, and substitution rate into one 0-100 trust score per tag to gate decisions.
Read → GlossaryHow do you configure historian compression sensibly?
Learn the two-stage pipeline, store audit-critical tags raw, size deadbands from noise, and validate by reconstruction.
Read → GlossaryWhat Is a Continuous Aggregate and How Is It Different From a Query-Time Rollup?
An automatically and incrementally maintained pre-aggregated table that makes repeated dashboard queries fast.
Read → GlossaryWhat Does the COUNT Aggregate Tell You in a Historian Query?
How counting samples per bucket exposes data completeness and collector health before value aggregates mislead.
Read → GlossaryWhat Is Dashboard Drill-Down?
The interaction that moves an operator from an enterprise roll-up to site, equipment, and a single tag trend.
Read → GlossaryWhat is a dashboard template in SCADA?
One screen layout bound to many sites by parameter, so each asset gets an identical view driven by its own tags.
Read → GlossaryWhat Is Data Backfill (Gap Filling)?
How buffered data recovered after an outage is inserted into history at its original timestamps.
Read → GlossaryWhat Is Data Completeness in a SCADA Historian?
The share of expected samples actually captured over a period - the headline coverage KPI for historian data.
Read → GlossaryWhat Is Data Contextualization?
Wrapping raw values in units, asset, location, and quality metadata so a number becomes meaningful, usable data.
Read → GlossaryHistorian & Data / Data Integrity / Data Gaps
How historians mark and query around genuine missing intervals versus stale flatlines, and why gaps are not interpolated.
Read → GlossaryWhat Is a Data Lifecycle Policy for Moving Time-Series Data Between Storage Tiers?
Automated aging rules that move data hot to warm to cold to deletion on a schedule as it ages.
Read → GlossaryWhat Is Data Normalization?
Bringing readings onto common units and scales - engineering-unit conversion and statistical scaling - for trustworthy analytics.
Read → GlossaryWhat Is a Data Quality Flag?
Metadata marking a value good, bad, stale, or uncertain - so bad data is excluded rather than silently corrupting analytics.
Read → GlossaryWhat Is a Data Rollup?
Pre-computed hourly and daily summaries stored beside raw data to speed long-range queries and reports.
Read → GlossaryWhat Is a Database Connector in SCADA?
The component that logs tags to and reads recipes from an external SQL database over ODBC or JDBC.
Read → GlossaryWhat Is a Dead-Letter Queue?
A holding queue for messages that repeatedly fail, so they neither block the flow nor vanish silently.
Read → GlossaryHistorian & Data / Compression / Decimation vs Compression
Why keeping every Nth sample loses spikes and aliases, and how signal-aware compression avoids it with bounded error.
Read → GlossaryDedicated historian box or a shared VM?
The historian is I/O-bound: share a VM only at low data rates, and give it a dedicated disk tier once tag count, retention, or query load grows.
Read → GlossaryWhat Is Device Fleet Management in IIoT?
Running hundreds of remote gateways as one fleet: health telemetry, grouping, bulk config, and remote diagnostics.
Read → GlossaryWhat Is Device Provisioning in IIoT?
Securely registering new field gateways with a cloud platform via identity, certificates, and zero-touch onboarding.
Read → GlossaryWhat Is Digital Twin Fidelity?
How closely a twin mirrors reality, and the tradeoff between high-fidelity physics and lightweight data-driven models.
Read → GlossaryWhat Is Double Chronometry?
The two-timer pulse-interpolation method that lets a small-volume prover resolve fractional meter pulses.
Read → GlossaryWhat Is Downsampling Time-Series Data?
Reducing millions of points to a chart's pixel width with min/max or largest-triangle methods without hiding spikes.
Read → GlossaryWhat is a duplicate timestamp in a historian?
Two values for the same tag at the same time; historians overwrite, reject, or keep both, and unresolved duplicates corrupt aggregates.
Read → GlossaryWhat Is Edge Analytics?
Running thresholds, aggregation, and ML inference at the gateway to cut latency and cellular bandwidth.
Read → GlossaryWhat is edge buffer backpressure?
How a gateway slows or sheds acquisition as its forward buffer fills, degrading gracefully not crashing.
Read → GlossaryWhat Is an Edge Gateway Device?
The rugged compute box between field devices and the cloud doing protocol translation, buffering, and secure links.
Read → GlossaryWhat is an edge historian ring buffer?
A fixed-size circular store that buffers unsent samples and overwrites the oldest data when full.
Read → GlossaryWhat Is an Enterprise Service Bus?
A central backbone that routes, transforms, and mediates messages among many enterprise applications.
Read → GlossaryWhat Is Exception Reporting?
Reports that surface only out-of-limit conditions - management by exception - and how it differs from report-by-exception telemetry.
Read → GlossaryWhat Is Exception vs Compression Deadband?
The two distinct deadband stages in a historian: the exception test at the collector versus compression at the archive.
Read → GlossaryWhat is a filtered summary query in a historian?
Aggregate computed only over the time a condition was true, such as average pressure while the compressor ran.
Read → GlossaryWhat is flow measurement validation, estimation, and editing (VEE)?
The validation, estimation, and editing quality gate analysts run on raw EFM data before volumes are booked.
Read → GlossaryWhat Is Tank Gauge Table Interpolation?
The calculation that finds exact volume for a level between strapping-table rows, done continuously by an ATG.
Read → GlossaryWhat Is GC Component Normalization?
How a chromatograph scales mole percents to sum to 100, the acceptance window, and why it can mask calibration drift.
Read → GlossaryWhat is a historian annotation?
Text note attached to a value or time that adds context without changing the value, audited and never compressed away.
Read → GlossaryHistorian & Data / Data Integrity / Historian Backfill
Inserting recovered or buffered data into the archive after the fact, and the ordering and recompression it forces.
Read → GlossaryWhat is a historian backfill window?
Configurable span within which the archive accepts past-timestamped writes; too narrow a window silently drops late data.
Read → GlossaryHistorian Collector
The interface that reads tags from field devices and SCADA and streams them into a process historian, with buffering and deadband filtering.
Read → GlossaryWhat is a historian compression ratio?
Share of scanned values a historian stores after filtering; outliers from the normal high range flag a mis-tuned tag fast.
Read → GlossaryWhat is historian data reprocessing?
Re-running calculated tags and rollups over a window after backfill or a correction so derived values stay consistent.
Read → GlossaryHow do you export historian data over ODBC?
Query the historian over ODBC by tag, time, and interval in raw or interpolated mode, and avoid full-archive scans.
Read → GlossaryWhat Is Historian Federation?
Querying many site historians as one without copying all their data into a single central store.
Read → GlossaryWhat is historian IOPS and disk sizing?
The write side of a historian: sample rate times tag count sets a sustained IOPS load that usually needs SSD or NVMe.
Read → GlossaryWhat is a historian mirror?
Collector writes the same stream to two independent archives so either can serve queries and survive loss of the other.
Read → GlossaryHow does a historian mirror resync after an outage?
Detects the window one member missed offline, copies the missing archive data back, and verifies both copies match.
Read → GlossaryWhat is a historian query index?
Lookup that maps tags and time ranges to archive blocks so queries seek instead of scanning; when to rebuild it.
Read → GlossaryHistorian & Data / Collection / Historian Scan Rate
How often the collector samples a source before compression, the oversampling tradeoff, and how it differs from PLC scan cycle.
Read → GlossaryHow Do You Size Historian Storage Capacity?
Estimating disk needs from tags, sample rate, bytes per value, and retention, then applying compression.
Read → GlossaryWhat is a historian tag scan group?
Tags bundled by collection frequency so a collector polls each group on its own interval, balancing load.
Read → GlossaryWhat is a historian write throttle?
Archive-side limit on ingest rate so a burst of collectors flushing buffers cannot overwhelm I/O or stall live data.
Read → GlossaryWhat is a historical overlay on a trend?
Placing a past window like yesterday or a golden run over the live trace to compare against a reference.
Read → GlossaryThe HMI and the historian disagree: which is right?
Live display and stored history use different mechanisms: compression, aggregation, timing, or a stale screen.
Read → GlossaryWhat Is Idempotency in Data Integration?
Making writes safe to repeat so retries and duplicate messages never double-count or re-fire actions.
Read → GlossaryHow Does a Time-Series Database Compress Data With Delta and Run-Length Encoding?
Lossless on-disk encoding - delta-of-delta timestamps, XOR and run-length values - that shrinks storage without dropping points.
Read → GlossaryWhat Is an Integral Aggregate and How Does It Turn a Rate Into a Total?
Integrating a rate over a window by trapezoidal area to get an accumulated total like volume or energy.
Read → GlossaryWhat Is an Interpolated vs Stepped Tag?
The per-tag flag that decides whether a historian slopes between points or holds the last value flat.
Read → GlossaryWhat Is a KPI Cascade?
How a top-level target decomposes into contributing metrics across sites and equipment for drill-to-root-cause.
Read → GlossaryKPI Dashboard
The screen that rolls up production, uptime, and alarm health into a few at-a-glance metrics that actually drive decisions.
Read → GlossaryWhat Is a KPI Target & Threshold?
How targets and warning or critical thresholds are set, and how they differ from process alarm limits.
Read → GlossaryHistorian & Data / Tags / Lab & Manual Entry Tags
Sparse, hand-entered values like lab assays and tank gauges, and how historians handle their irregular, out-of-order arrival.
Read → GlossaryWhat Is Last-Known-Value?
The sample-and-hold query mode that returns the most recent stored sample at any timestamp.
Read → GlossaryWhat Is Linear Interpolation in a Historian?
How a historian rebuilds a value at any timestamp from the two bounding compressed points.
Read → GlossaryWhat is link aggregation (LAG) in industrial switches?
Bundling several physical links into one logical LAG for bandwidth and uplink redundancy between managed switches.
Read → GlossaryWhat Is Last Observation Carried Forward for Filling Time-Series Gaps?
The forward-fill rule that repeats the last value across gaps, safe for state tags, risky for stalled sensors.
Read → GlossaryWhat is Log Aggregation in OT?
Collecting logs from PLCs, HMIs, and network gear into one tamper-evident store as the raw material a SIEM analyzes.
Read → GlossaryWhat Is a Logarithmic Axis on a Trend?
A decade-scaled trend axis that keeps values spanning many orders of magnitude readable across the whole range.
Read → GlossaryHistorian & Data / Compression / Lossless vs Lossy
Deadband and swinging-door as bounded-error lossy storage, and how the deviation guarantees a maximum reconstruction error.
Read → GlossaryWhat Is the Largest-Triangle-Three-Buckets Algorithm for Downsampling?
The LTTB algorithm picks the most visually significant points so a downsampled chart still looks like the full data.
Read → GlossaryWhat is a manual data entry tag in a historian?
Tag with values typed in by a person, timestamped and flagged as manual, with an audit trail of who entered them.
Read → GlossaryWhat Is Master Data Management in OT?
Keeping one golden record per asset so SCADA, historian, CMMS, and ERP agree on the same wells and equipment.
Read → GlossaryWhat is medallion architecture in an industrial data lake?
The bronze, silver, and gold layering of raw, cleaned, and aggregated SCADA telemetry that keeps raw data auditable while serving BI.
Read → GlossaryWhat Is Min-Max Decimation and Why Does It Preserve Spikes on a Trend?
Keeping the high and low of each pixel column so a downsampled trend still shows transients averaging would erase.
Read → GlossaryHow do you monitor an aggregate conveying system?
Make the belt protection trips visible and located, trend idler and pulley bearing temperatures, watch the drive load and material flow, and prove the protection path works.
Read → GlossaryWhat is MQTT to time-series database ingestion?
The subscriber-writer pipeline that decodes MQTT payloads, maps them to measurements, and batches them into a time-series store.
Read → GlossaryWhat Is a Multi-Pen Trend Group?
A saved chart of related tags plotted together on one time axis to reveal cause, effect, and correlation.
Read → GlossaryWhat is the difference between NB-IoT and LTE-M?
A head-to-head on throughput, latency, mobility, and power for fixed sensors versus mobile assets.
Read → GlossaryHow do you normalize timestamps in a historian?
Store in UTC, keep source over receipt time, file late data by event time, and handle daylight saving at display only.
Read → GlossaryWhat Is a North-Bound Interface?
The upward-facing side of a gateway or SCADA server that exposes field data to enterprise and cloud systems.
Read → GlossaryWhy Does Treating a Data Gap as Zero Instead of Null Corrupt Your Reports?
Zero is a measured none, null is no data; summing gaps as zero understates totals, null-aware aggregates skip them.
Read → GlossaryWhat is OPC UA to SQL database integration?
Piping OPC UA subscription updates into SQL tables with mapping, batching, quality preservation, and store-and-forward buffering.
Read → GlossaryHistorian & Data / Data Integrity / Out-of-Order Data
What breaks when points arrive earlier than stored data, from buffering or clock skew, and how historians reorder them.
Read → GlossaryWhat is a patch rollup and how is it staged for OT?
How OT mirrors cumulative rollups, tests them on a staging replica, and follows approved-patch lists before the plant.
Read → GlossaryWhat Is a Percentile Aggregate and When Do You Use P95 Instead of an Average?
How P95, P99, and the median expose peak loads and tail behavior that an average smooths flat.
Read → GlossaryWhat is a plot-values query in a historian?
Display retrieval returning min, max, first, and last per pixel-interval so long trends draw fast without losing spikes.
Read → GlossaryWhat Is a Process Digital Twin?
A live simulation of the process itself, fed by real-time SCADA data, for what-if analysis and optimisation.
Read → GlossaryWhat is protocol normalization at the edge?
Converting many field protocols into one consistent tag model and payload before publishing upstream.
Read → GlossaryWhat Is Raw Versus Aggregate Retention in a Historian?
Setting how long a historian keeps full-resolution raw samples versus pre-computed aggregate rollups.
Read → GlossaryWhat Is the Difference Between a Regular and an Irregular Time Series?
Evenly spaced fixed-interval logging versus exception-based data at uneven times, and why the difference breaks averaging.
Read → GlossaryWhat is a responsive SCADA dashboard?
One screen definition that reflows for phone, tablet, and desktop, serving field and control room without a mobile app.
Read → GlossaryWhat Is REST API Integration in SCADA?
Exposing tag data over HTTP and JSON so any tool can pull SCADA values without a native driver.
Read → GlossaryREST API or OPC UA for IT integration?
A selection guide comparing web-native access against the OT information model, with a rule for choosing per consumer.
Read → GlossaryWhat Is a Retention Policy in a Time-Series Database?
The mechanism that automatically expires and drops data past a set age, configured per measurement as a TTL.
Read → GlossaryWhat is a role-based KPI dashboard?
A tailored view per role - operator, engineer, executive - drawn from the same data, right metrics per seat.
Read → GlossaryWhat Is a Rolling Average?
A moving average that smooths noisy data over a sliding window - simple vs exponential, and how window size trades off.
Read → GlossaryWhat Is the Difference Between a Sampling Interval and a Logging Interval?
How often a sensor is read versus how often a value is stored, and why the gap saves space but can miss spikes.
Read → GlossaryWhat is a SCADA to cloud data lake pipeline?
The pipeline that lands raw and aggregated telemetry in object storage as Parquet, partitioned by asset and time for analytics.
Read → GlossaryWhat is SCADA to ERP master data synchronization?
Aligning tag identities with ERP material numbers and functional locations via cross-reference tables so postings land right.
Read → GlossaryWhat is a scheduled historian data export?
Recurring automated job that writes a tag set to a file or endpoint on a schedule for downstream feeds and handoffs.
Read → GlossaryWhat Is Series Cardinality and Why Does It Blow Up Historian Performance?
The count of unique tag and label combinations that drives memory and index cost and can explode with careless labeling.
Read → GlossaryWhat Is Serverless Computing?
Running code on demand without managing servers, billed per execution, ideal for event-driven IIoT tasks.
Read → GlossaryHow do you set historian retention tiers?
Keep raw for the recent window, roll older data into aggregates, and protect regulated data with its own retention policy.
Read → GlossaryWhat Is a South-Bound Interface?
The field-facing side of a gateway that polls PLCs, RTUs, and meters over Modbus, DNP3, and OPC UA.
Read → GlossaryWhat Does a Standard-Deviation Aggregate Reveal About a Process Tag?
How a per-bucket stddev quantifies process variability and noise for control-loop health and SPC.
Read → GlossaryWhen Should a Query Use Step Instead of Linear Interpolation?
The query-time rule: staircase for digital and setpoint tags, sloped line for continuous analog measurements.
Read → GlossaryWhat Is Swinging Door Compression?
Step through the SDT algorithm: how the upper and lower doors pivot and collapse to trigger a stored point.
Read → GlossaryWhat Is Master Data Management for SCADA Tags?
Keeping one authoritative, governed definition of every tag so historian, HMI, and reports never drift apart.
Read → GlossaryWhat Is a Tag Namespace?
The hierarchical naming scheme that keeps thousands of SCADA tags unique and organized by site, asset, and measurement.
Read → GlossaryWhat is a target-vs-actual KPI tile?
A tile showing a measured value against its target with the variance, for an at-a-glance on-plan signal.
Read → GlossaryWhat Is Tiered Historian Retention (Hot, Warm, Cold)?
Storing recent data hot, mid-age data warm, and old data cold to balance query speed against cost.
Read → GlossaryWhat Is Time-Bucket Aggregation?
How a historian query groups raw samples into fixed intervals with min, max, avg, and sum functions.
Read → GlossaryWhat Is a Time-Weighted Average?
Why compressed data must be averaged by area under the curve, not as a plain mean of stored points.
Read → GlossaryHistorian & Data / Aggregation / Totalizer Tags
How historians integrate a rate into a running total and handle rollover, resets, and daily-boundary flow totals.
Read → GlossaryWhat is a traffic-light KPI dashboard?
A red-amber-green status view that lets you manage a multi-site fleet by scanning for color.
Read → GlossaryWhat is a trend annotation on an HMI?
An operator note pinned to a point on a trend so the reason behind a change travels with the data.
Read → GlossaryWhat Is a Trend Cursor on an HMI?
A movable line that reads exact values and times off a trend, with dual cursors measuring change and rate.
Read → GlossaryWhat Is Trend Deviation?
Detecting when a value drifts from its expected trend or baseline - catching slow degradation that fixed alarms miss.
Read → GlossaryWhat is a trend group and how do you configure one?
A how-to on defining reusable named trend groups: choosing tags, setting scales and axes, and a time span.
Read → GlossaryWhat is a live-versus-historical trend overlay?
Plotting a tag's live values over its own past run on shared axes to spot drift and abnormal behavior.
Read → GlossaryWhat Is a Trend Pen?
Each plotted line on a SCADA trend, named for the ink pens of chart recorders.
Read → GlossaryTrending
Plotting a variable over time to reveal drift, patterns, and correlations - the everyday tool for diagnosing process behavior.
Read → GlossaryWhat is an upsert write pattern for SCADA database integration?
Loading SCADA readings idempotently with MERGE keyed on tag plus timestamp so replays and late data correct rows.
Read → GlossaryShould a Historian Store UTC or Local Time?
Why storing UTC and displaying local avoids the DST duplicate and missing hour across multi-timezone sites.
Read → GlossaryWhat Is a Cloud Gateway?
The edge device that bridges field protocols to the cloud - protocol translation, store and forward, security, and its role in cloud SCADA.
Read → GlossaryWhat Is a Data Lake?
A central store for raw data of any type - schema-on-read, data lake vs warehouse vs historian, and where lakes fit in oil and gas analytics.
Read → GlossaryWhat Is a Tag Database?
The master list of every SCADA data point - tags, types, metadata, and why the tag database is the heart of any SCADA configuration.
Read → GlossaryWhat Is a Time-Series Database (TSDB)?
The database built for timestamped sensor data - compression, time-range queries, TSDB vs relational, and its role in SCADA historians.
Read → GlossaryWhat Is Deadband Compression?
How historians drop insignificant changes to store less - simple deadband vs swinging door, and choosing compression without losing real events.
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