Hi @William_Ortiz,
The assoc_type fields take on constants defined in PHP in classes/core/Application.inc.php and lib/pkp/classes/core/PKPApplication.inc.php in lines like this:
define('ASSOC_TYPE_ARTICLE', 0x0000101);
0x0000101 is hexadecimal notation, which corresponds to 257 in decimal. Not all ASSOC_TYPE_... constants are used in the metrics table, as you’ve already noticed; these are general purpose constants used in many parts of OJS.
Regards,
Alec Smecher
Public Knowledge Project Team