It should be noted that while 7PK presents a unified perspective, it is not viewed as unified with respect to 1000's model of the world. For example, 7PK's "input validation" kingdom specifies many issues as children such as SQL injection (CWE-89) and XSS (CWE-79). This practice is also followed in the Development view. However, input validation is treated as a protection mechanism within 1000, which is separated (through chaining relationships) from issues that could be fixed by input validation. Vulncat's perspective is not unified in the 1000 model, either; it has categories such as "Denial of Service" (which are consequences in 1000's model), "Log Forging" (an attack), and "Buffer Overflow: Off-by-One" (a chain).
Some specific consequences (e.g. NULL pointer dereference) are assigned CWE identifiers, but generally as the final link in a chain. Within CWE, a NULL dereference is always treated as the result of some other error, such as the failure to check an error condition. This approach ignores the pathological case in which a programmer directly provides the NULL constant as an argument (perhaps as a way to make a quick exit from an application).
Mutually Exclusive
The 7PK paper does not state whether mutually exclusive classification is a goal. The layout does not imply that the same item could have multiple parents. However, there are cases in which items could be classified in multiple ways. Vulncat's language-specific breakdown at the top level reuses the 7PK kingdoms at the next level below the individual languages.