Learn about ExDesc (extended descriptor) - RDBMS
- Last UpdatedAug 19, 2025
- 2 minute read
- PI System
- Interfaces
The ExDesc attribute configures a variety of run-time settings, two of which are included in every interface and are described in the following table.
Note: Keywords must be specified in upper case.
|
Keyword |
Description |
Example |
|---|---|---|
|
ALIAS |
Map PI point names to corresponding names in the RDBMS. Case-sensitive. For details about configuring aliases, see Reading target tag names from the database (distribution) in this document. |
/ALIAS=Level123 or /ALIAS="Level 123" |
|
GETPOINTS |
At startup, cache only those points, that pass the filter defined by this keyword. The SQL statement, defined in the Extended Descriptor of the tags with Location4=-1 or -2, will only be executed when an attribute had changed for the cached points. See Learn about rec how to record PI Point database changes for PI Interface for RDBMS in this document. If no /GETPOINTS keyword found, the interface will cache points with point source, the given instance runs with. REM: The filter syntax complies with the WHERE condition syntax the PI SDK's GetPoints () method accepts. |
/GETPOINTS="tag='abc*'" (React onto PiPoint attribute changes for points their names start with abc only.) |
|
PERFORMANCE_POINT |
When set, such point stores the amount of time, in seconds, that it takes an interface to complete a scan for a particular scan class. The lower the scan time, the better the performance. |
PERFORMANCE_POINT For details, refer to the PI Universal Interface (UniInt) Framework User Guide. |
|
SQL |
Specify the query for the tag. Enclose the query in double quotes and terminate it with a semicolon, followed by any placeholders, separated by white space. For details examples of queries, see Learn about SQL examples for PI Interface for RDBMS in this document. |
/SQL="SELECT timestamp, value, status FROM table1 WHERE timestamp >? ORDER BY timestamp ASC;" P1=TS |
|
TRANSACT |
If more than one SQL statement is specified for the tag, the queries are executed as a single transaction (committed or rolled back together). |
/TRANSACT |
|
TRIG or EVENT |
For event-driven input points: each time the specified point changes, the SQL query is executed. If the point name contains spaces, you must enclose it in single quotes. If there are subsequent parameters, you must specify a comma after the /EVENT specification. Valid conditions:
|
/EVENT=sinusoid, … or /EVENT=sinusoid anychange, … |
Note: To assign values to replaceable parameters in SQL queries, you specify placeholders in the ExDesc attribute. Replaceable parameters in queries are indicated by question marks.
ExtendedDescriptor Length
Depending on the version of the PI API and the Data Archive, this interface supports an ExDesc attribute whose length is at most 80 or 1023 characters. The following table indicates the maximum length of this attribute for all the different combinations of PI API and Data Archive versions.
|
PI API |
Data Archive |
Maximum Length |
|---|---|---|
|
1.6.0.2 or later |
4.370.x or later |
1023 |
|
1.6.0.2 or later |
Earlier than 3.4.370.x |
80 |
|
Earlier than 1.6.0.2 |
4.370.x or later |
80 |
|
Earlier than 1.6.0.2 |
Earlier than 3.4.370.x |
80 |
Performance Points
For UniInt-based interfaces, the extended descriptor is checked for the string PERFORMANCE_POINT. If this character string is found, UniInt treats this point as a performance point.