update README.md

0f148daf · Wanxin Li · 42f7b264 · 0f148daf
Commit 0f148daf authored 5 years ago by Wanxin Li
--- a/README.md
+++ b/README.md
@@ -77,4 +77,48 @@ valid.
 Also the Makefile only has two commands, `make` and `make clean`. `make` will
 create both the SQLPParser and Parser programs to do what was described above.
 Maybe this should be changed in the future to be separate but we'll leave that
-discussion for the future.
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+discussion for the future.
+
+Added in Spring 2019:
+Entity descriptions for algebra in lisp form. There are two sorts of operators:
+(1) operators producing normal tables with an ordered finite sequence of attribute
+names, and (2) operators producing “column tables”, where tuples are a possibly
+infinite set of “SQLP column name”/“constant” pairs.
+
+<query> (1)
+	( select <set-or-bag> <limit> (as-list <as> … ) <body> )
+	( union <set-or-bag> <limit> (query-list <query> … ) )
+
+<set-or-bag>
+	distinct
+	all
+
+<limit>
+	( limit <integer-constant> )
+	( no-limit )
+
+<as>
+	( as <column> <attribute-name> )
+
+<body> (2)
+	<pred>
+	( atom <table-name> <var> )
+	( natural-join-list <body> … )
+	( sub-query <query> <var> )
+
+<pred>
+	( equal <term> <term> )
+	( less-than <term> <term> )
+	( less-than-or-equal <term> <term> )
+	( exists <body> )
+	( not <pred> )
+	( and-list <pred> … )
+	( or-list <pred> … )
+
+<term>
+	<column>
+	( integer <integer-constant> )
+	( string <string-constant> )
+
+<column>
+	( column <var> ( attribute-name-list <attribute-name> … ) )
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