---
manual: IM 36K10P10-01EN
title: Class Description Language - Traditional
edition: 4th Edition, Feb. 2026 (first summarized from the 3rd Edition, Sep. 2023)
version: R1.05 (first written for R1.03)
status: R1.05 re-check 2026-10-09: manual text unchanged except contact information (full word diff); CIENG_TANK compiled and ran on the R1.05 test server 2026-10-08 (SIGNAL to an existing item, SIGNAL … FROM … MAKE, PROMPT, TRIGGER VALUE). From docs; PROLOG/ATTRIBUTE/PROMPT/ERROR, SIGNAL to an existing item and SIGNAL … FROM … MAKE, TRIGGER VALUE, the SECTION constant, transitional >=:, PRINT and runtime attribute change verified with CI-Eng-Sample class CIENG_TANK on 2026-09-30; everything else from docs
---

# Traditional PROCESS Service language (R1.05)

**R1.05 (4th Edition, Feb. 2026):** only contact information was added; a word-by-word diff
with the 3rd Edition found no other change. Section numbers are unchanged. The class source
template `%TLS_DAT_PATH%\opc_src_tpl.asc` and the user-function sources `tls\src\opc_usr*.c`
are identical on R1.03 and R1.05.

Summary in own words; section numbers refer to the manual. Engineering of classes and objects:
`IM36K10L10-01EN.md` and skill `class-object-engineering`.

## 1. Structure (§1, §11.1)

```
CLASS <name>;                 { name max 15 characters }
  PROLOG                      { optional class prolog: runs when an object is CREATED }
    <local declarations, CONTAINS, ATTRIBUTE, PROMPT, SIGNAL, statements>
  BODY                        { needed only when there is a class prolog }
    <global declarations: CONSTANT, VAR, TIMER, ALARM, ITEM, FOR>
    METHOD <name>;            { method name max 50 characters }
      ENTRYCONDITION <cond>;  { optional guard }
      <local declarations>
      PROLOG <statements>     { optional: first run / after going on-line }
      BODY <statements>
      EPILOG <statements>     { optional: when deactivated }
    ENDMETHOD <name>;
ENDCLASS <name>;
```

- Comments: `{ … }`, may span lines.
- All methods of an active object run "simultaneously" (like tasks), not in order.
- Method parts by state: becoming active → prolog + body; staying active → body; becoming
  inactive (entry condition false or object off-line) → epilog (Table 1.3-1).
- **Control item** (optional, per object): blocked = methods suspended; off-line = stopped,
  on-line again = start as new. Its value is `STEP` (below).
- `SEQUENCE`/`SUBSEQUENCE` are old synonyms of `CLASS`/`METHOD`; do not use.
- Enterprise classes (Enterprise Engineering Module): extra `MAKE` fields `CREATE_ITEM`,
  `PUT_IN_HISTORY`, `ALARM_DETECTION` = `MASTER_ONLY` / `DELEGATE_ONLY` / `MASTER_AND_DELEGATE`;
  ignored in local classes (§1.6).

## 2. Declarations (§2, §11.2)

| Declaration | Syntax (short) | Notes |
|---|---|---|
| Constant | `CONSTANT a := 1, b := 2.5;` | Type from the expression |
| Variable | `VAR x [INTEGER\|FLOAT\|STRING];` | Default FLOAT; numbers convert, strings and numbers do not mix |
| Timer | `TIMER t [TRIGGER];` | Value = seconds left; `t'status` STOPPED / RUNNING / EXPIRED (initial EXPIRED). Assign seconds to start; 0 → EXPIRED. `TRIGGER` runs the object on expiry |
| Alarm | `ALARM a [TRIGGER];` | Value = alarm text, `a'status` NORMAL/A1/A2/A3 (OR `ACKNOWLEDGE`), `a'priority`. Needs `ALARM-ITEMS` in `opc.sup` (not set on the installed system) |
| Attribute | `ATTRIBUTE n [OBJECT\|CLASS] [INTEGER\|FLOAT\|STRING];` | In class prolog only. OBJECT (default) = per object; CLASS = one value for all objects. Kept across restarts. Name max 15 |
| Prompt | `PROMPT n QUERY "text";` / `NOPROMPT path;` | Asks the value of an OBJECT attribute when an object is created. Declaration, not a statement |
| Containment | `CONTAINS alias := other_class;` | Include another class; access `alias.signal`, nest `a.b.signal` |
| Signal | see §3 | In class prolog only |
| Item / For | `FOR [node:]inst[.unit]; ITEM tag [TRIGGER type];` | Fixed item names (first two section levels only); prefer SIGNAL |

Limits: identifiers 50 characters (class, attribute, signal, function names 15); string values
max 255 characters.

## 3. Signals (§2.3, §11.2.8)

A signal links the object to an item whose name is computed **when the object is created**,
so each object can use different items.

```
SIGNAL LEVEL := SECTION || ".LEVEL" TRIGGER VALUE;            { existing item }
SIGNAL VOLUME := FROM "<template item>[;<station>:<template point>]" MAKE
    "DESCRIPTION" EQUAL "text"  "NAME" EQUAL "<new item name>"  … ;  { create the item }
```

- Types `INTEGER`, `FLOAT` (default), `STRING` after the signal name.
- `FROM … MAKE`: copies the template item (and point) and overrides the listed fields; any field
  of `ITEM_DF`, `SUB_ITEM_DF`, `ITEM_HIS_DF` and the station's `POINT_DF` may be used (e.g.
  `"STATION"`, `"POINT"`, `"IO_ADDRESS"`, `"ALARMING" EQUAL ON`, `"PROCESS_LIST" EQUAL "1,3"`).
  Storage: `"GROUP_NAME" EQUAL "<group>"` followed by its storage fields (`"STORE_VALUE"`,
  `"ON_VALUE_CHANGE"` …); up to 4 groups; order matters. A template's own history membership is
  **not** copied.
- Without `"NAME"` the item is named `<object>.[<containment path>.]<signal>` and missing
  sections are created (verified: object `CI-Eng-Sample.TANK1.CALC`, signal `VOLUME` →
  item `CI-Eng-Sample.TANK1.CALC.VOLUME`). Sub-items always need a name.
- Items and sections the object created are **deleted with the object** (verified), unless the
  object has `LEAVE_ITEMS`; existing items are only unlinked.
- An empty template name creates nothing: the signal stays unattached (`sig'attached` false).
- Creating a point that already exists fails the object creation.
- Use `||` to build names; a comma in a SIGNAL statement is read as a list separator.
- Release notes: if the object sits at root level `SECTION` is empty — build names as
  `IF SECTION = "" THEN tag ELSE SECTION || "." || tag`; prefer automatic naming.

**Trigger types** (combine with `|`): `VALUE`, `STATUS`, `OPTION`, `UPDATE`, `FIRST`, `PIT`,
`LIMIT`, `QUALITY`.

**Signal attributes** (`sig'attr`; plain `sig` = value): `VALUE`, `OLD_VALUE`, `STATUS`,
`CONTROL_STATUS`, `OPTION_STATUS` (`OPT_BLOCKED`, `OPT_OFF_LINE`, … with bitwise operators),
`MERGED_STATUS`, `ALARM_TYPE`, `ACKNOWLEDGED`, the four limits, `DEADBAND`, `QUALITY`,
`UPDATE_TIME`, `ID_*`, `SECTION`, `TAG`, `SUB`, `APPLICATION_INFO[i]`/`_SIZE`/`_FLAG`,
`LOCKED`, `ATTACHED`. Which are writable differs between the manual's two tables (§2.3 vs
§11.2.8); value and limits are writable in both. To set value and status together use
`SIG_UPDATE`.

**Object constants**: `NOW` (GMT, float seconds), `NODE`, `INSTALLATION`, `UNIT`, `SECTION`
(object's section path — verified), `TAG` (object's tag), `CLASS`.

## 4. Statements and expressions (§3–5, §11.4–11.5, §11.7)

| Statement | Example | Notes |
|---|---|---|
| Assignment | `x := 12;` | To variable, signal (writes the item), attribute, timer, alarm |
| Add | `x :+ 5;` / `x :+ -5;` | |
| IF | `IF c THEN … [ELSE …] ENDIF;` | Nestable |
| TRIGGER | `TRIGGER 60;` / `TRIGGER CLASS alias;` | Run again after n s (last one wins); trigger a contained class |
| PRINT | `PRINT "text ", x;` | To the message log when `PRINT = YES` (installed). A single `%` cuts the message; `%%` prints `%` (ISS-025) |
| ERROR | `ERROR "text";` | In a method: logs and stops this run. In the class prolog: **object creation is refused** and the text is returned (verified: `dssqld` `.qlo` shows `OPC-E-INFO, <text>`) |
| STEP | `ENTRYCONDITION STEP = 2; … STEP := 3;` | Value of the control item; state machine between methods |

Operators, highest first: unary `+ -`; `NOT ~`; `* /`; `+ -`; string `||` and `,` (comma also
joins numbers); `= <> =: <>:`; `< > <= >= <: >: <=: >=:`; `&`; `^`; `|`; `AND`; `XOR`; `OR`.
**Transitional** operators (`=:`, `>=:` …) are true only on the evaluation where the comparison
**becomes** true (edge detection) — verified: `LEVEL >=: 80.0` fired for 85 and again for 81
after 70, not for 90 after 85. `TRUE`/`ON` and `FALSE`/`OFF` are the same.

`IF TRIGGERED BY GROUP|SIGNAL|TIMER|TRIGGER|ALARM|ONCE` tells why the object ran;
`TRGSIG(sig)`, `TRGTIM(t)`, `TRGALM(a)` name the exact source. A trigger group with interval
**ONCE** runs the object once when it is created, reset, its class reset, or PROCESS starts —
good for initialisation (`ENTRYCONDITION TRIGGERED BY ONCE;`).

Format strings for `STRING(x, "fmt")` (§11.7.4): `9` digits, `0` leading zeros, `+` sign,
`.` decimal point, `EEEE` exponent; dates (seconds since 1970) `D DD DDD M MM MMM Y YY YYYY
Hh Mm Ss P`; `\` escapes; `%…` C-style (`%5.2f`); empty = `%g`.

## 5. Built-in functions (§6.2, §11.6)

- Maths: `ABS`, `TRUNC`, `SQRT`, `POWER`, `EXP`, `LOG`, `LOG10`, `SIN`/`COS`/`TAN`,
  `ARC…`, `…HYP`, `RANDOM`.
- Time: `NOW`, `GMT`, `LCT` (local time), `ADDMONTH`, `DAYS`.
- Strings/conversion: `LENGTH`, `LEFT`, `MIDDLE`, `RIGHT`, `STRING`, `INTEGER`, `FLOAT`.
- Trigger info at trigger time: `TRGSIG_VALUE`, `TRGSIG_OLD_VALUE`, `TRGSIG_STATUS`,
  `TRGSIG_QUALITY`, `TRGSIG_UPDATE_TIME`, limits, `…_STR_VALUE` etc.
- Signal functions: `SIG_UPDATE(sig, value, status, add)`, `SIG_UPDATE_TIME(…, time)` (sends
  time to ITM; size its queue), `SIG_OFFLINE(sig, on)`, `SIG_LOCK`, `SIG_FORCE_ALARM_STATE`,
  `SIG_GETSUB(sig, avg, reset)` (read and reset a sub-item in one step), `SIG_GET_…`/`SIG_SET_…`
  by attribute id (ids from Yokogawa).

**User functions** (§7): class named `FUNCTIONS` (no objects from it) with
`FUNCTION [INTEGER|FLOAT|STRING|VOID] name; ARG a FLOAT, …; <CONSTANT/VAR>; <statements>;
RETURN v; ENDFUNCTION name;`. Max 10 arguments, passed by reference; a user function with a
built-in's name overrides it.

## 6. Datasets from a class (§12)

- Basic: `DSS_READ_STRING|INTEGER|FLOAT(dataset, record NAME, field, result)` and
  `DSS_UPDATE_STRING|INTEGER|FLOAT(…)`; `result` 1 = OK.
- Advanced: `id := DSS_OPEN(dataset, "F1, F2", "rudi", result)` or `DSS_OPEN_ALL`;
  `DSS_READ_EQUAL(id, name)`, `DSS_READ_NEXT`, `DSS_SET_FILTER` / `DSS_REMOVE_FILTER`,
  `DSS_GET_…` / `DSS_PUT_…` on the field buffer, then `DSS_UPDATE`, `DSS_INSERT`,
  `DSS_DELETE`; always `DSS_CLOSE(id)` (otherwise memory leaks). `DSS_ERROR_LOG(on)`.
- Only STRING, INTEGER, FLOAT data types are supported.

## 7. AGA gas calculations (§13)

`AGA_INIT`, `AGA_COMP` (composition), `AGA_CALC`, `AGA_3_METER`, `AGA_CONE`, `AGA_PULSE`,
`AGA_8_GROSS`, `AGA_9_…` (ultrasonic), `AGA_R_…` result getters, `AGA_ERROR`. Not practiced;
see the manual's §13.2 example if needed.

## 8. Examples in the manual (Appendix 1)

`TWIN_UNIT_CONTR` (STEP state machine with timers, transitional operators and limit changes)
and `SENSOR`/`FLUID_VESSEL` (containment). Reserved words: Appendix 2.