Don Box and Data

6 years ago I was in a WebServices DevCon in Boston and Don Box did a presentation about data, where he started playing with SQL and doing things like 'insert into people select * from products'. As People/Products had the same schema (Id/Name), it worked fine (I'm not sure if that was the actual example, but it was something like that). The object-oriented-strongly-typed heads in the audience were nodding saying that he was doing something 'bad'.

I also remember a blog post from Don from some time ago (that I couldn't find) saying that XML schemas were relative to the consumer. One XML document can comply with a lot of XML schemas. What was important was not that it had a specific structure, but that it had a structure that was compatible with what you needed. I could have an XSD that says that I need 'Id' and 'Name' and I don't care about the rest, and if an XML document had it, then it was good enough for me.

I remembered this when he was describing the typing in M. Basically, in M if two types have the same properties, they are equivalent. Just as in SQL. And in XSD. And in duck typing.