Comment by foltik

Agreed. Any language that wants to use the fact graph is going to have to “interpret” the chosen DSL anyways, and JSON is more ubiquitous and far simpler to parse than XML. Also way cheaper in the sense that the article uses it (how many langs can you parse and walk an XML document in off the top of your head? what about JSON?)

To see why JSON is simpler, imagine what the sum total of all code needed to parse and interpret the fact graph without any dependencies would look like.

With XML you’re carrying complex state in hash maps and comparing strings everywhere to match open/close tags. Even more complexity depending on how the DSL uses attributes, child nodes, text content.

With JSON you just need to match open/close [] {} and a few literals. Then you can skim the declarative part right off the top of the resulting AST.

It’s easy to ignore all this complexity since XML libs hide it away, and sure it will get the job done. But like others pointed out, decisions like these pile up and result in latency getting worse despite computers getting exponentially faster.