Work Breakdown Structure. A product-oriented family tree division of hardware, software, services, and other work tasks which organizes, defines, and graphically displays the product to be produced as well as the work to be accomplished to achieve the specified product. Project Summary Work Breakdown Structure (PWBS). A summary work breakdown structure (WBS) tailored to a specific defense material item by selecting applicable elements from one or more summary WBSs or by adding equivalent elements unique to the project in accordance with MIL-HNDBK 881 (latest revision). Contract Work Breakdown Structure (CWBS). The complete WBS for a contract, developed and used by a contractor within the guidelines of MIL-HNDBK 881 (latest revision) and according to the contract's work statement. The CWBS includes the levels specified in the contract and the contractor's extension.