Using External ID-based Tags in the OPC Item for the CygNet OPC Server

The CygNet OPC Server supports the resolution of OPC items by an External ID. The External ID is an optional property of a CygNet point record (part of the CygNet Point Reference property). The CygNet OPC Server can parse and resolve ExternalID-based CygNet tags passed in as OPC items.

OPC Item Tag Format

The External ID OPC item tag format is the following:

SITE.SERVICE:::MixedCaseExternalId{;PROPERTY}

where

• SITE.SERVICE::: — Represents the CygNet Site and Service to be queried. The three colons between the "SITE.SERVICE" and the "MixedCaseExternalId" portion in the OPC item are required. The "SITE.SERVICE:::" portion of the OPC item can be omitted. See Omitting the Site.Service Specifier in the OPC Item for the CygNet OPC Server for more information about this option.
• MixedCaseExternalId — Represents a point's ExternalId field, configured in the External ID property of the point configuration record. Including the "MixedCaseExternalId" portion in the OPC item will return a point's ExternalId field when the CygNet OPC Server performs a QueryProperties action. See the character limitations below.
• {;PROPERTY} — Represents the OPC property being queried. ";EXTERNALID" is a valid property identifier when specifying an OPC item. The ";PROPERTY" portion of the OPC item is always optional. See Available Point Properties for the CygNet OPC Server for a list of possible properties.

MixedCaseExternalId Characters

All printable ASCII characters are allowed in the "MixedCaseExternalId" portion of the OPC item, except for the semi-colon character (';'). The following characters are allowed:

• Any mixed-case alpha-numeric characters (A-Z,a-z,0-9)

• Any special characters (!\"#$%&'()*+,-./:<=>?@[\\]^_`{|}~ ), including the <space> character ( ), but excluding the semi-colon character (';')

• There is a 256 character limit.

Add to PNT Index and Reindex

If you plan to use an External ID as an OPC tag, we recommend that you add the following custom index to the PntAppl.ddl file to optimize performance when resolving OPC items by an External ID. Follow this by reindexing the PNT database using ReIndexESE (run as admin).

DEFINE INDEX ID=EX_INDEX, NAME=PNT_EX_INDEX, VERSION=1, RECORD_ID_BYTE=27, PREFIX=EX, DESCR="External ID", ITEM=(EXTID.ExtId, LENGTH=79);

See Adding a New Index to a DBS-Based Service for more information about adding an index and reindexing a service database.