YDB AIM 

Overview 

Applications need metadata. By providing an API to manage metadata, and enable content-based access to data, the YottaDB AIM (Application Independent Metadata) plugin removes the need for each YottaDB application to create its own separate framework.

Quickstart 

As a YottaDB plugin, AIM requires YottaDB. You can install YottaDB and AIM together:

mkdir /tmp/tmp ; wget -P /tmp/tmp https://gitlab.com/YottaDB/DB/YDB/raw/master/sr_unix/ydbinstall.sh
cd /tmp/tmp ; chmod +x ydbinstall.sh
sudo ./ydbinstall.sh --utf8 --aim

Omit the --utf8 option if you do not want UTF-8 support installed. If you already have YottaDB installed, use sudo $ydb_dist/ydbinstall --aim --plugins-only --overwrite-existing to install or reinstall the AIM plugin without reinstalling YottaDB.

When used to install Octo, ydbinstall / ydbinstall.sh automatically installs AIM, as it is a requirement for Octo.

Installation 

If you don't use the Quickstart method, you can install YDBAIM from source. In addition to YottaDB and its requirements, YDBAIM requires cmake, gcc, git, make, and pkg-config. Clone the YDBAIM repository, and then install the plugin, using the following commands:

git clone https://gitlab.com/YottaDB/Util/YDBAIM.git YDBAIM-master
cd YDBAIM-master
mkdir build && cd build
cmake ..
make && sudo make install

Metadata 

Cross References 

As an example consider a global variable whose first subscript is the year a US President assumed office and the second subscript is the year that President left office, with values such as:

^USPresidents(1797,1801)="John||Adams" and
^USPresidents(1835,1839)="John|Quincy|Adams"

Data Cross References

The call $$XREFDATA^%YDBAIM("^USPresidents",2,"|",3) cross references the third piece of node values (last names), with the cross reference global having values such as ^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(3,"Adams",1797,1801)="", ^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(3,"Adams",1835,1839)="", and many others including ^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(3,"Obama",2009,2017)="".

Suppose only Presidents who left office in the 19th century should be cross referenced. A local variable node such as cent19(2)="1801:1899" can be created, and passed by reference, and $$XREFDATA^%YDBAIM("^USPresidents",.cent19,"|",3) produces the two cross references as above, but in a different global variable name since the trigger signatures are different. Unlike the first cross reference, this does not cross reference Barack Obama who assumed office in 2009 and left in 2017.

Suppose only Presidents who assumed office in the 19th century should be cross referenced, a local variable cent19 would instead have the node cent19(1)="1801:1899" to indicate that only first subscripts should be cross referenced if they are in the 19th century, but the local variable root node cent19=2 should be set to indicate that two subscripts should be cross referenced. In this case, the call $$XREFDATA^%YDBAIMD("^USPresidents",.cent19,"|",3) generates a cross reference that includes John Quincy Adams, but not John Adams who assumed office in 1797, which is in the 18th century.

To cross reference all three names, the call $$XREFDATA^%YDBAIM("^USPresidents",2,"|","1:3") is used to generate the following cross references for the two President Adams:

^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(1,"John",1797,1801)=""
^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(1,"John",1835,1839)=""
^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(2,"",1797,1801)=""
^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(2,"Quincy",1835,1839)=""
^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(3,"Adams",1797,1801)=""
^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(3,"Adams",1835,1839)=""

Since the first President Adams record does not include a middle name, the corresponding record has an empty string ("") subscript. Any region to which ^%ydbAIM* global variables are mapped must have NULL_SUBSCRIPTS set to ALWAYS. Since the subscripts will include pieces of global nodes, or even entire global nodes, it would be prudent to set YottaDB's maximum key size (1019 bytes) for that region.

Note

Subscript specifications which are not canonical numbers should be quoted. So to cross reference the first piece with "|" separator of ^%ydbocto("tables","pg_catalog","pg_attribute",*):

YDB>set sub=4,sub(1)="""tables""",sub(2)="""pg_catalog""",sub(3)="""pg_attribute"""
YDB>set xref=$$XREFDATA^%YDBAIM("^%ydbocto",.sub,"|",1)

to create the cross reference:

YDB>write xref
^%ydbAIMDvjlGbD84bQ5u5hXGOtIe37
YDB>

Setting a value now creates the cross reference:

YDB>set ^%ydbocto("tables","pg_catalog","pg_attribute",100)="ABC|DEF"

YDB>write $query(@xref@(1,"ABC",""))
^%ydbAIMDvjlGbD84bQ5u5hXGOtIe37(1,"ABC",100)
YDB>

Subscript Cross References

AIM can also cross reference subscripts. To search values of subscripts other than the first subscript requires using $ORDER() to loop through higher level subscripts, which can be time-consuming for a large dataset. The call $$XREFSUB^%YDBAIM("^USPresidents",2,2) cross references the second subscript of the two-subscript global variable ^USPresidents, with values such as:

^%ydbAIMSrNrMckj7LkdFXjsHkuT91D(2,1913,1909)=""
^%ydbAIMSrNrMckj7LkdFXjsHkuT91D(2,1921,1913)=""
^%ydbAIMSrNrMckj7LkdFXjsHkuT91D(2,1923,1921)=""

The first subscript of ^%ydbAIMSrNrMckj7LkdFXjsHkuT91D is the subscript number of the cross reference, in this case 2 for the second subscript. The second subscript of ^%ydbAIMSrNrMckj7LkdFXjsHkuT91D are values of the cross referenced second subscript, and the third subscript is a corresponding first subscript for the cross referenced first subscript. So ^%ydbAIMSrNrMckj7LkdFXjsHkuT91D(2,1921,1913)="" says that there is a node ^USPresidents(1913.1921).

Example - Using a Subscript Cross Reference

This illustrates the use of XREFSUB() to replace scanning of application subscripts.

Consider a global variable ^X(a,b,c) where an application needs to find all nodes whose second subscript (b) meets some criterion. In SQL terms, this is like a table with a primary key consisting of three columns, and statement SELECT a,b,c WHERE b meets some condition. This is illustrated in the M program scandemo2.m; equivalent programs can be written in any supported language.

The program generates a global with a number of nodes. The number can be specified on the command line to run the program, e.g., yottadb -run scandemo2 10000, with the number defaulting to 100,000 if not specfied. Each of the subscripts is a random number from 0 through 999,999. The program then scans the global variable to find nodes (i.e., SELECTs from the table) that meet four different criteria. For each criterion, it scans in two ways, without using XREFSUB() and using XREFSUB(). In each case it prints the time taken and the number of nodes/rows found; the latter must be the same regardless of how the global variable is scanned.

The first is to identify all nodes where b>750000, i.e., a simple numerical scan.
The second is to scan all nodes where b follows "700000", i.e., a lexical scan. For example, US zip codes are numeric, but should be ordered lexically (a numeric scan would ignore leading zeroes).
The third is a scan based on the value of a 1:1 transformation function, i.e., f(b) satisfies some criterion. A sample use case of such a transformation function is one where times are stored in local time, but need to be converted to UTC for processing / selection. In the scandemo2 program, the 1:1 transformation is the square root of b ($$FUNC^%SQROOT(b)), and the selection criterion is nodes where the square root is greater than 750.
The fourth is a scan based on the value of a many:1 transformation function. A hypothetical use case might be the checksum of other values, or where the values are the orbital parameters of a celestial object, and the transformation function is the next date that the object is likely to pass within 100,000 kilometers of Planet Earth. In the scandemo2 program, the many:1 transformation function is the sum of the digits of the second subscript, and the selection criterion is nodes where the sum is greater than 30.

Sample output:

$ yottadb -run scandemo2 10000
Traversal without XREFSUB() took 4,209 microseconds for 2,495 nodes/rows
Traversal with XREFSUB() took 2,933 microseconds for 2,495 nodes/rows
Traversal without XREFSUB() using string collation took 4,961 microseconds for 2,795 nodes/rows
Traversal with XREFSUB() using string collation took 3,494 microseconds for 2,795 nodes/rows
Traversal without XREFSUB() using a 1:1 transformation function took 7,896 microseconds for 4,335 nodes/rows
Traversal with XREFSUB() using a 1:1 transformation function took 5,769 microseconds for 4,335 nodes/rows
Traversal without XREFSUB() using a many:1 transformation function took 8,049 microseconds for 3,139 nodes/rows
Traversal with XREFSUB() using a many:1 transformation function took 3,041 microseconds for 3,139 nodes/rows
$

Statistics 

The optional parameter stat can be used to instruct AIM that the application wishes to compute and maintain statistics. There are two types of statistics (the default, stat=0, is cross references only and no statistics):

stat=1: statistics on the count of each value. Thus the call $$XREFDATA^%YDBAIM("^USPresidents",2,"|","1:3",,,,1) would compute and maintain nodes such as ^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(-1,"John")=4 to indicate that "John" appears as the first piece four times (the first subscript is the negative of the piece number).
stat=2: in addition to the count of each value, also counts the number of different values, and also a total count of the number of values maintained. Thus, the call $$XREFDATA^%YDBAIM("^USPresidents",2,"|","1:3",,,,2) would compute and maintain nodes such as ^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(-3)=39 to indicate that there are 39 distinct last names and ^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(11)=135 to indicate that there are 135 nodes maintained (as of 2021, the 45 former US Presidents times 3 names for each ex-President).

Example - Statistics

YDB>set x=$$XREFDATA^%YDBAIM("^USPresidents",2,"|","1:3",,,,2)

YDB>set z="" f i=1:1:5  s z=$o(@x@(-1,z)) zwr @x@(-1,z) ; count of each value
^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(-1,"Abraham")=1
^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(-1,"Andrew")=2
^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(-1,"Barack")=1
^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(-1,"Benjamin")=1
^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(-1,"Bill")=1

YDB>zwrite %ydbAIMDf1x7fSMuGT4HtAEXAx0g65(-3:-1),^(11) ; number of distinct values and number of total values
^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(-3)=39  ; 39 distinct last names
^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(-2)=14  ; 14 distinct middle names/initials
^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(-1)=31  ; 31 distinct first names
^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(11)=135 ; a total of 135 nodes maintained

YDB>

Statistics can be used to optimize queries. For example, if one wants a query where the first name is George (^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(-1,"George")=3), middle initial is W. (^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(-2,"W.")=1) and the last name is Bush (^%ydbAIMDf1x7fSMuGT4HtAEXAx0g65(-3,"Bush")=2), it would make sense to look at the middle initial first (since its count is one). This approach minimizes the number of global accesses.

Consider another example, a global variable that contains all of the U.S. State Capitals and you would like to find out which capitals are named after the Presidents. In this case it would make sense to look at the last names of the Presidents first, since there are 39 distinct last names and 50 distinct state capitals.

Application Schema Type 

The above description describes the most straightforward type of application schema, where all application nodes with metadata managed by AIM have the same number of subscripts. However, the freedom that global variables provide to application designers means that different applications design their schemas in different ways.

The default type parameter in the call to XREFDATA() creates metadata for straightforward case above. Adding schemas consists of:

Creating new trigger templates as needed, and creating triggers from new and existing trigger templates.
Adding logic in XREFDATA() to create the initial metadata.

With a value of 1 or 3 for type, AIM creates and manages metadata for a schema used by the VistA Fileman software.

For a Fileman schema (i.e., type 1 or type 3), when

the last subscript specification specifies a constant;
a node with that constant subscript does not exist; and
other nodes exist at the level of that constant subscript, i.e., there is at least one other node whose subscripts are identical except for that constant last subscript.

AIM creates and maintains metadata nodes for the requested pieces using the empty string ("") as the last subscript intead of the specified constant. For example, the node ^ORD(100.01,0)="ORDER STATUS^100.01I^99^16" when cross referenced with the call $$XREFDATA^%YDBAIM("^ORD",.sub,"^",1,0,0,1,0,1,0) where sub(1)=100.01,sub(2)=":"" """,sub(3)=.1 produces the cross reference ^%ydbAIMDu1oVZCaYBv7SgPmwQNP201(1,"",0)="" even though there is no ^ORD(100.01,0,.1) node.

While type 1 and type 3 both apply to Fileman schemas, the cross references for type 1 are the actual data, whereas the cross references for type 3 use Transformation Functions.

Forcing String Collation 

In AIM cross reference globals, the cross referenced application data are subscripts. This means that the cross references are ordered by M subscript collation: the empty string, followed by canonic numbers, followed by other strings. While this is appropriate for the majority of applications, for applications whose data can include canonic numbers and strings, cross references should be ordered as strings. Examples include United States zip codes and international telephone numbers, e.g., with default collation, the M code:

YDB>set zip(1)="01801",zip(2)="19355",xref=$$UNXREFDATA^%YDBAIM("^zip",1,,,,,,,,)

Creates the cross reference:

^%ydbAIMDxYLWlHuPLdyPGfSMaZdn8B(0,19355,2)=""
^%ydbAIMDxYLWlHuPLdyPGfSMaZdn8B(0,"01801",1)=""

which is incorrect, as 01801 should sort before 19355. Using the force parameter:

YDB>set ^zip(1)="01801",^zip(2)="19355",xref=$$XREFDATA^%YDBAIM("^zip",1,,,,,,,,1)

Each cross reference is prefixed with # and the nodes are sorted correctly:

^%ydbAIMDQ2cA8Z4cVwjtYEGFKYXY64(0,"#01801",1)=""
^%ydbAIMDQ2cA8Z4cVwjtYEGFKYXY64(0,"#19355",2)=""

Notes:

Applications using AIM globals, for example, $ORDER(), ydb_subscript_next_s() / ydb_subscript_next_st() and related functions in other languages should remove the leading "#" from the subscripts reported by AIM when traversing application globals, and prepend a leading "#" to locate cross referenced data.
YottaDB recommends using 1 as the force parameter for forcing string collation, to allow other values to be used for other types of forcing.

Transformation Functions 

The most common use of cross reference is to find global nodes that contain the data being cross referenced, for example to traverse that data in order. But cross references are useful for many reasons. For example:

There are multiple formats for storing dates and times, and comparing values directly can slow Octo queries. But if the cross reference for each time stamp is its UNIX time (i.e., its $ZUT value), then comparing time stamps, or choosing dates and times within a range becomes a much simpler proposition. This is a 1:1 transformation function.
Cross referencing a hash or checksum allows an application to locate the original data for the hash or checksum. This is potentially a many:1 transformation function.

Transformation is accomplished by provding the M code for a function in the force parameter with a value of 2 or 3 for the type parameter. For example, if "$$ABC^DEF()" is the value passed in force, triggers for cross referenced nodes will use the value returned by the transformation function as the value to cross reference. When the function is called at runtime by the trigger, the first parameter is the actual node or piece value, e.g., $$ABC^DEF("2024-02-21T13:31:48.05098021+07:00") would yield the actual cross-referenced value if the timestamp in the global node is 2024-02-21T13:31:48.05098021+07:00. If the function requires additional parameters, they can be specified as comma separated values for the second and subsequent parameters, e.g., "$$ABC^DEF(,1,""two"")". As local variables cannot be passed to triggers, these additional parameters can only be constants, global variable references, or function calls whose parameters are constants, global variables, or function calls. Application code that needs to pass local variable values to the transformation function should use $ZTWORMHOLE.

For example, with the ^USPresidents global variable mentioned earlier, the node ^USPresidents(1797,1801)="John||Adams" would generate the cross refence ^%ydbAIMDHgTwbHgcmyZEIfADw7Xq07(3,"0x5d156e592ad2e9a83eb48043c59213d0",1797,1801)="" with a call to $$XREFDATA^%YDBAIM("^USPresidents",2,"|",3,0,0,0,0,2,"$ZYHASH()".

A value of 2 for type, informs AIM that the schema for the global nodes is an ordinary schema; a value of 3, informs AIM that the global nodes have a Fileman schema.

Functions 

XREFDATA()

XREFDATA() computes and maintain cross references for nodes values or pieces of node values, of a global variable at a specified subscript level.

The format for XREFDATA() is as follows:

$$XREFDATA^%YDBAIM(gbl,xsub,sep,pnum,nmonly,zpiece,omitfix,stat,type,force)

where,

gbl is the global variable name, e.g., ^ABC
xsub is a specification of the subscripts to be cross referenced. There are three cases:
- xsub has a positive integer value at the root, and no subtrees (i.e., $DATA(xsub) is 1): The value specifies the level (number of subscripts) of the global variable for which the cross reference is to be created, with all subscripts at each level to be included in the cross reference. In this case, the actual parameter can be a literal or a variable passed by value. In other cases it must be passed by reference.
- xsub has no value at the root, but positive integer subscripts (1), (2), (3), etc (i.e., $DATA(xsub) is 10): The subscripts of the local variable specify the values of the global variable subscript to be cross referenced, using the same syntax as trigvn field of trigger definitions. The last subscript defines the level of the global variable to be cross referenced. Any omitted intervening subscript (e.g., if the local variable has nodes (1) and (3) but not (2)) means that all subscripts at that level should be included in the cross reference.
- xsub has both a value at the root, as well as positive integer subscripts (i.e., $DATA(xsub) is 11): This is similar to the previous case, except that if the value at the root exceeds the last subscript, that is the level of the global variable to be cross referenced. For example, if the local variable has nodes (1) and (3) but the value at the root is 5, five subscripts of the global variable will be cross referenced. A value at the root smaller than the last subscript is ignored, so with the subscripts above and a value of 2 at the root, three subscripts will be cross referenced.
Other cases (e.g., non integer subscripts of xsub) raise errors.
sep is the piece separator for values at that node; if unspecified or the empty string, the cross reference is for entire node values.
pnum is a semi-colon separated list of integer piece numbers for which cross references should exist; ignored for cross references of entire node values, effectively a no-op if pieces specified are already cross-referenced.
nmonly, if 1, means just return the cross reference global variable name but don't set triggers or compute cross references.
zpiece, if 1, means that $ZPIECE() should be used as the piece separator instead of $PIECE(). AIM can have cross references for the same nodes with both options; the cross references are in different global variables.
omitfix, if 1, instructs XREFDATA() to omit from the subscripts of the cross reference any subscripts of the application global that are fixed constants because the code to traverse the application global using the cross reference will include those known fixed subscripts when making the access. If not specified, omitfix defaults to 1.
stat if 1 or 2 says the metadata should include statistics, as described above under Statistics.
type, defaulting to the empty string, specifies the application schema for which AIM is being asked to compute and maintain metadata.
force, defaults to the empty string. A value of 1 specifies that AIM cross references should prepend a hash (#) to the data being cross referenced. If type is 1 or 3, force specifies either string collation or a transformation function for an application global using the Fileman schema; if type is 2, force specifies a transformation function. See Forcing String Collation.

The relationship between type and force is shown below. Combinations of values other than those shown are reserved.

type
		0, "", or omitted	1	2	3
force	0, "", or omitted	Normal schema; normal M ordering	Fileman schema; normal M ordering
	1	Normal schema; forced String ordering	Fileman schema; forced string ordering
	Function			Normal schema transformation function ordering	Fileman schema; transformation function ordering

Metadata about the cross reference itself is stored in nodes of the cross-reference global variable as follows:

The root node is the application global variable name (the gbl parameter of the function call).
Subscripted nodes are:

(0) space separated $ZUT of the time the cross reference was completed, $JOB of the process, $ZYRELEASE of the YottaDB release number and, a format version number for the metadata.

(1) number of cross-referenced subscripts of the application global variable.

(2) piece separator, if any. The empty string specifies whole-node cross references.

(3) & (4) piece numbers, in the form of a bit-map like string, prefixed with "#" to prevent numeric conversion, e.g., the value for pieces 2, 4 and 5 would be "#01011", the empty string for an cross reference of the entire node. The (3) node identifies the piece numbers for which cross referencing is complete whereas (4) identifies those for which triggers exist. If they are not equal, it means that a process created triggers, but is still working on cross referencing existing global nodes. It is also possible that the process terminated, or was terminated, before completing its work.

(5) 1 means $ZPIECE() was used for pieces; the default empty string is $PIECE().

(6) SET trigger for this cross reference.

(7) KILL trigger for this cross reference; see also comment for (12) below.

(8) ZKILL trigger for this cross reference.

(9) 1 means that omitting fixed subscripts was requested, whether or not any subscripts were actually omitted.

(10) if 1 or 2 means that statistics are maintained, as specified by the stat parameter.

(11) unused, but reserved.

(12) & up - triggers for KILLs of higher level nodes.

Applications can read and use the above metadata, but should not attempt to alter it. Changes can result in unpredictable and/or undesirable behavior.

XREFSUB()

XREFSUB() computes and maintain cross references for subscripts of a global variable at specified subscript levels.

The format for XREFDATA() is as follows:

XREFSUB(gbl,xsub,snum,nmonly,omitfix,stat,type,force)

where

gbl, xsub, nmonly, omitfix, and stat are the same as for XREFDATA().
snum uses the same syntax as pnum for XREFDATA() to specify subscripts that should be cross-referenced. Unlike pnum, it is not optional. Any subscript that is specified by snum must be part of xsub, e.g., if snum specifies cross referencing of the third subscript, xsub must specify a global variable with at least 3 subscripts.

type defaults to the empty string, which is also equivalent to 0. A value of 2 indicates that force is a transformation function. Unlike XREFDATA(), XREFSUB() does not implement special logic for Fileman subscripts.

force defaults to the empty string, which is equivalent to 0. A value of 1 when type is defaulted or zero indicates that AIM cross references should prepend a hash (#) to the cross reference, which forces string collation even for numbers (e.g., US zip codes). If type is 2, force should be a string specifying a transformation function for cross references (see Forcing String Collation).

The relationship between type and force is shown below. Combinations of values other than those shown are reserved.

type
		0, "", or omitted	2
force	0, "", or omitted	Normal schema; normal M ordering
	1	Normal schema; forced String ordering
	Function		Normal schema transformation function ordering

Metadata about the cross reference itself is stored in nodes of the cross-reference global variable as follows:

The root node is the application global variable name (the gbl parameter of the function call).
Subscripted nodes are:

(0) space separated $ZUT of the time the cross reference was completed, $JOB of the process, $ZYRELEASE of the YottaDB release number and, a format version number for the metadata.

(1) number of cross-referenced subscripts of the application global variable.

(2) unused, but reserved.

(3) & (4) subscript numbers, in the form of bit strings manipulated by $ZBIT*() functions. The (3) node identifies the piece numbers for which cross referencing is complete whereas (4) identifies those for which triggers exist. If they are not equal, it means that a process created triggers, but is still working on cross referencing existing global nodes. It is also possible that the process terminated, or was terminated, before completing its work.

(5) unused but reserved.

(6) SET trigger for this cross reference.

(7) KILL trigger for this cross reference; see also comment for (12) below.

(8) ZKILL trigger for this cross reference.

(9) 1 means that omitting fixed subscripts was requested, whether or not any subscripts were actually omitted.

(10) if 1 or 2 means that statistics are maintained, as specified by the stat parameter.

(11) unused, but reserved.

(12) & up - triggers for KILLs of higher level nodes.

Applications can read and use the above metadata, but should not attempt to alter it. Changes can result in unpredictable and/or undesirable behavior.

LSXREFDATA() / LSXREFSUB()

LSXREFDATA() lists metadata for a data cross reference, all data cross references for a global variable, or all data cross references. LSXREFSUB() lists metadata for a subscript cross reference, all subscript cross references for a global variable, or all subscript cross references.

The format for LSXREFDATA() / LSXREFSUB() is as follows:

DO LSXREFDATA^%YDBAIM(lvn[,gbl])
DO LSXREFSUB^%YDBAIM(lvn[,gbl])

where,

lvn is a local variable passed by reference. In that local variable, the function describes all cross references as follows:
- The first subscript is the cross reference global variable name, e.g., ^%ydbAIMDgBPWsnL76HLyVnlvsrvE19 or ^%ydbAIMSrNrMckj7LkdFXjsHkuT91D. The value of its root node (i.e., with no subscript) is the application global variable name, e.g., ^USPresidents.
- Nodes with positive integer second subscripts have metadata about the metadata. These are described in XREFDATA() and XREFSUB().
Nodes of lvn other than those corresponding to reported cross references remain unaltered.
gbl is a global variable name. There are three cases:
- It is an application global variable name, e.g., ^USPresidents. In lvn as described above, the function returns all data or subscript cross references for that global variable, depending on whether the function is LSXREFDATA() or LSXREFSUB().
- It starts with ^%ydbAIMD or ^%ydbAIMS. In lvn, the function returns information about the specified cross reference.
- It is omitted or the empty string (""). In lvn, the function returns information about all data or subscript cross references, depending on whether the function called is LSXREFDATA() or LSXREFSUB().

UNXREFDATA() / UNXREFSUB()

UNXREFDATA() removes all data metadata; UNXREFSUB() removes all subscript metadata
UNXREFDATA(aimgbl) and UNXREFSUB(aimgbl) where aimgbl is an AIM metadata global variable, removes the metadata stored in that AIM global. Note that an AIM global variable stores either data metadata or subscript metadata, but not both.
UNXREFDATA(gbl) where gbl is an application global name removes all data metadata for that application global; UNXREFSUB(gbl) does likewise for subscript metadata.

UNXREFDATA() and UNXREFSUB() provide an API for removing specific cross references. The APIs mirror those of XREFDATA() and XREFSUB(), allowing for removal of a specific cross reference by replicating the paramaters used to call the functions that created the cross references in the first place. The APIs are as follows and the parameters are described in XREFDATA() and XREFSUB(). Note that some parameters are specific to one function or the othyer.

DO UNXREFDATA^%YDBAIM(gbl,xsub,sep,pnum,nmonly,zpiece,omitfix,stat,type,force)
DO UNXREFSUB^%YDBAIM(gbl,xsub,snum,nmonly,omitfix,stat,type,force)

where,

gbl is the global variable name, e.g., ^ABC for which the metadata is to be removed. If omitted, all cross references and triggers for cross references are removed as discussed above.
xsub is a specification of the subscripts in the cross reference to be removed.
sep is the piece separator for values at that node; if unspecified or the empty string, the cross reference signature is entire node values.
pnum and snum exists to allow the parameters of UNXREFDATA() and UNXREFSUB() to match those of XREFDATA() and XREFSUB() and are ignored. Note that regardless of the values of these parameters, calling the functions removes the metadata for all pieces, and all subscripts.
nmonly is ignored.
zpiece, must match that of the XREFDATA() call that set up the cross reference.
omitfix and stat are ignored.
type and force must match the XREFDATA() or XREFSUB() that set up the criss reference.

VERSION()

VERSION() provides semantic version information for AIM, consisting of a major version number and a minor version number, separated by a period.

A change to the major version, number indicates a breaking change, which for AIM primarily means a change to the metadata schema. There are separate major version numbers for data and subscript metadata.
A change to the minor version number indidates an upward-compatible (non-breaking) change. The minor version number is common to data and subscript metadata.

There is one optional parameter, as follows:

VERSION(str) where str is case-insensitive "TEXT" or "DATA" reports the major version number for selected type of metadata, as well as the minor version number.
VERSION() reports the major version as the sum of the text and subscript metadata, as well as the minor version number.

For example:

YDB>write $$VERSION^%YDBAIM
3.1
YDB>

Operational Considerations 

Any region to which ^%ydbAIM* global variables are mapped should have NULL_SUBSCRIPTS set to ALWAYS, and implement standard null collation.
YottaDB recommends setting journaling and replication to the YDBAIM region to match the settings of the application database region(s) that AIM cross references. This is because AIM sets triggers in those regions to maintain AIM metadata in sync with application data.
If the YDBAIM region and application data become out of sync with each other, use UNXREFDATA() followed by XREFDATA() to resynchronize them.
If ydb-treat-sigusr2-like-sigusr1 is set, on receipt of a SIGUSR2, %YDBAIM terminates indexing of data and returns to its caller; otherwise it ignores SIGUSR2. This facilitates use of %YDBAIM by Octo.