Thanks for the reply.
CASCADE means that the data is deleted also in parent and child tables, RESTRICT means that only parent data is deleted. Changing the default RESTRICT does nothing, the data is still there
Any other option?

UPD: i've managed to delete data with

UPDATE TABLE table SET column = NULL

But issue is still open, why %DELDATA do nothing

As far as I understand from your answer, I have no choice but to apply some hacks to my data. This is unfortunate. I was thinking about using a hash too. I think I will do that.

The code piece that reading file 
 

If '$IsObject(pStream) {
            Set tFilename = pStream
            Set pStream = ##class(%IO.FileStream).%New()
            Do pStream.Open(tFilename,,pTimeout,"UTF-8", .tStatus)
            If $$$ISERR(tStatus) Quit
        }

Thank you so much. You were very helpful.

Thanks for the answer. If i understand correctly, this specific line should be place inside REST API for make audit to work? So, if i don't have any access to the REST API code the desired audit is not possible?

Hi! 

Thanks for your answer. I've read the docs through out couple times to find the explanation but did not find any. I'll try to express my self more crystal

Suppose i have some myUI app in my IRIS instance. This myUI using DeepSee REST API to get the data. I need to get track of any activity on that UI at any time (in general when a user requests the data)

What should i need as the audit source? 

myUI? Some endpoint from API? Some class executing by this endpoint?
Documentation says:
"Event Source*

The component of the InterSystems IRIS instance that is the source of the event. For InterSystems IRIS events, this is “%System” or “%Ensemble”. For user-defined events, the name can be any string that includes alphanumeric characters or punctuation, except for colons and commas; it can begin with any of these characters except for the percent sign. This can be up to 64 bytes."
Ok, what string? How any random string can be serve as audit source? Same for the audit type 
I get that the string represents my app or part of it, but how that will track actions from myUI?

It is very useful! At first it gave out "The web application does not exist." Then I create it manually and then the response was "Illegal web request".

This is something to start with! Thank you.

The WritePivotVariablesForCube upon debug however return proper response 

{

"children":[

{

"name":"Year",

"caption":"Year",

"defValue":2018,

"context":"literal",

"desc":""

}

]

}

Yes, exactly like your example

/MDX2JSON/Test gives an adequate response yes
How can i retrieve a logical name of a cube?

Looks simple, but I'm still having trouble with it. First of all, do I have to be logged into Intersystems Servers in Intersystems Tools for debugging? Secondly, every time I start debugging I get an error.

What should I do about it? It prevents me from working.

Any console with ability to display debug information. IRIS Terminal is too bulky to operate effichancy. I am searching for a simple ways to investigate what variables hold what and what return this or another method

%Get Members For Filter class method. In particular restriction to show only 2500 members in filter list.

Thank you for your answer! This video helped.

Thank you for your answer!