One of the general principles of JRules is, that you should call the rules engine with all the necessary information if possible. From a performance perspective, accessing the database during rule execution isn't a good idea. You might also lose the ability to use your rule app in a clustered environment. Also, decisions are less traceable and reproducible because it's harder to know what's in your database at any given moment.
Depending on how often your data changes, I suggest you add these values as a second input parameter and retrieve the data before you call the rules engine. The second possibility is to use the dynamic domain plugin to load those values from the database prior to deployment. But you would have to redeploy the ruleApp every time the data changes. With the dynamic domain plugin you can specify a data provider (e.g. Excel, MySQL etc.) and populate your BOM with the attributes contained in the database. These dynamic domain values show up as attributes and can be synced from the BOM-view in rule studio as well as from the teamserver:

In WODM (the successor of JRules 7.1) this functionality is build in, it's possible that this plugin is not part of the demo and has to be added to 7.1 individually.