You may notice that the new topic branch created in the prior chapter
Demos/Sportsbook/Football/England/All/ holds exclusively JSON topics. Using a source value directive we can selectively unpack the structure of those JSON topics to create new topics.
map ?Demos/Sportsbook/Football/England/All// to "<path(0)>/away win" as "<value(/away win)>".
Demos/Sportsbook/Football/England/All/Manchester United vs Arsenal. These topics contain the values of the field
away winwithin their parent topic. If that field is absent, no corresponding
away wintopic is created.
Notice the new value mapping clause
as <value(/away win)>, which extracts the field
away win from the source topic in creating the reference topic. This is a JSON Pointer.
Using the value mapping clause, it is possible to expose a subset of a dataset to the audience to achieve greater data efficiency. The reference topics can have different topic permissions, enabling you to share a subset of the dataset with more liberal permissions.
Summary: Use the value mapping clause
value() to extract parts of source topics into reference topics.
Next: Throttling reference topics.