# What is an HMI tag database?

In the HMI tag database, you can define data you want FactoryTalk View to monitor. There is one HMI tag database per HMI server. Each entry in the database is called an HMI tag. An HMI tag is a logical name for a variable in a device or in local memory (RAM) that is referenced in the HMI tag database.

All parts of the system use tag values. Graphics uses tag values to control the animation in a display or update a trend graph; Alarming monitors HMI tag values and compares them to "acceptable" limits; Data Log stores tag values to create a historical record.

HMI tags are required when you need extra information included with the tag value. This extra information can be a minimum/ maximum value range or value units. If you do not need this information, you can use direct references to tags in other data servers.

## HMI tags you do not create

A set of system tags is created automatically when you create an HMI server project, and stored in a folder called 'system' in the tag database.

- System tags - store information generated while the system is running, including alarm reset time and date, system time and date, and current user information. There are analog, digital, and string system tags. You can use them anywhere you use other types of tags, but you cannot edit system tags.

  Tip: | The maximum number of alarmable HMI tags allowed is 5000 per HMI server. Each graphic display can contain up to 1000 expressions or references to tags.

## See also

About HMI tag types

About data sources

Set up an HMI tag database

Log tag data

Keywords: HMI tag database