Update the schema documentation.

[dead/htsn-import.git] / doc / man1 / htsn-import.1

diff --git a/doc/man1/htsn-import.1 b/doc/man1/htsn-import.1
index 66506c6febaf300dd8be82ce7e5f9c1b624627fb..957382d5b077c57d8bc443da616636423121c684 100644 (file)
--- a/doc/man1/htsn-import.1
+++ b/doc/man1/htsn-import.1
@@ -68,19 +68,27 @@ that we import. For example, the documents corresponding to
 These top-level tables will often have children. For example, each
 news item has zero or more locations associated with it. The child
 table will be named <parent>_<children>, which in this case
-corresponsds to \(dqnews_locations\(dq.
+corresponds to \(dqnews_locations\(dq.
 .P
-To relate the two, a third table exists with name <parent
+To relate the two, a third table may exist with name <parent
 table>__<child table>. Note the two underscores. This prevents
-ambiguity when the child table itself contains underscores. As long we
-never go more than one level down, this system should suffice. The
-table joining \(dqnews\(dq with \(dqnews_locations\(dq is thus called
+ambiguity when the child table itself contains underscores. The table
+joining \(dqnews\(dq with \(dqnews_locations\(dq is thus called
 \(dqnews__news_locations\(dq.
 .P
-Wherever possible, children are kept unique to prevent pointless
-duplication. This slows down inserts, and speeds up reads (which we
-assume are much more frequent). The current rate at which the feed
-transmits XML is much too slow to cause problems inserting.
+Where it makes sense, children are kept unique to prevent pointless
+duplication. This slows down inserts, and speeds up reads (which are
+much more frequent). There is a tradeoff to be made, however. For a
+table with a small, fixed upper bound on the number of rows (like
+\(dqodds_casinos\(dq), there is great benefit to de-duplication. The
+total number of rows stays small, so inserts are still quick, and many
+duplicate rows are eliminated.
+.P
+But, with a table like \(dqodds_games\(dq, the number of games grows
+quickly and without bound. It is therefore more beneficial to be able
+to delete the old games (though an ON DELETE CASCADE, tied to
+\(dqodds\(dq) than it is to eliminate duplication. A table like
+\(dqnews_locations\(dq is somewhere in-between.
 .P
 UML diagrams of the resulting database schema for each XML document
 type are provided with the \fBhtsn-import\fR documentation.