There are a number of categories of references included in the References Table. These categories are listed below with their tags. SWEREFs are tagged to allow easy access to the members of a category in case there is a need to update some or all members of the category.
| Label | Meaning |
|---|---|
| npr | NASA Procedural Requirements |
| npd | NASA Policy Directives |
| hdbk | NASA Handbook |
| llis | Lessons Learned - includes entries in the LLIS database as well as documents that contain Lessons Learned and are referenced in the SWEHB |
| tp | Technical papers, presentations and other non-NASA documents |
| pa | Process Asset, typically from a Center. Some may be found in SPAN. |
| tng | Training courses |
| test | SWEREFs reserved for testing |
