how to relate Asset to SLA rules

how to relate Asset to SLA rules

hi:
there is a problem.
When i add a new request there is no option "Workstation Name",but only option "Asset".
But when i define SLA rules, in the option "Select Criteria" list,there is a item "Workstation Name",no item "Asset".
What should i do,when i want to relate "Asset" with SLA.



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