AVEVA Historian - SQL Server Standard CAL license count?

I should have noted this in my original reply, but there is not a strict requirement for SQL Server Standard based on the tag count, though at one time AVEVA did include that in larger Historian licenses. Historian is actually a very lightweight application as far as traditional SQL Server database applications go, and that will easily scale to the 2M tag limit for Historian using SQL Express without any material impact on data collection. 

Where SQL Express becomes more of a limiting factor is SQL query load, which is normally used for Historian Client Trend, AVEVA Reports, and other applications. Internally, a "tier 1" Historian also uses SQL for managing the "sync queue". The biggest benefit for SQL Server Standard will be in applications with a lot of concurrent SQL queries. System tags can give an indication of when an application is bound by SQL Express limitations (see: SysPerfSQLServerCPU, SysPerfSQLServerVirtualMBytes, SysPerfSQLServerPageFaults). The exact limits may vary by SQL Express release,

Since the time-series data isn't actually stored in database tables, applications using the REST interface or the .NET SDK will see minimal differences between Express and Standard, but they will still require a SQL CAL when using SQL Server Standard. 

Thanks Elliott.

Thanks Elliott.