In R12 apart from AWB ,there is yet another toolset which is called Transaction Account Builder aka TAB which normally used to derive default accounts for a particular transactions using sources , which is defined in the Accounting Methods Builder (AMB). 
Normally this derives accounting codes from the TAB which internally driven the AMB setup attributes.
This is used derive default accounts for transactions before they are accounted and then it is used the AMB to generate the accounts that appear in the accounting.
TAB only derives default accounts for transactions. These accounts may not be the ones that appear on the subledger journal entries since these are generated by the Create Accounting program based on the application accounting definitions.
What are key components
The TAB Components figure below shows the components
Moreover you can see the source and account derivation rules(ADD) are shared with the AMB which was discussed in one of the last post.
Will discuss some more details for this utility in some another post and we will try to compare how its different from Autoaccounting?
- R12 SLA: Analyzing Subledger Accounting 
- R12 SLA: From Product Accounting to Subledger Accounting 
- R12 SLA: Accounting Methods Builder 
- R12 SLA: Transaction Account Builder