1. Sequences in XQuery Core data structure of XQuery Date: 8/25/2009
Dan McCreary
President
Dan McCreary & Associates
(952) M D
Metadata Solutions

2. Copyright 2008 Dan McCreary & Associates
Agenda/Objective
What are sequences in XQuery?
Comparison with RDBMS/SQL
Why are they critical to understanding XQuery?
A Comparison with other List Processing Languages
Examples
Copyright 2008 Dan McCreary & Associates

3. Three Ways to Represent Data
Tables
Trees
Tabular data assumes that every column has homogeneous data
Each item has the same data type
Sequences are collections of any types of data
Copyright 2008 Dan McCreary & Associates

4. Table Columns Hold Similar Data
date
decimal
string
float
blob
integer
Columns must all have the same data type that is predefined in the Data Definition Language (DDL) using CREATE TABLE statements.
Copyright 2008 Dan McCreary & Associates

5. Copyright 2008 Dan McCreary & Associates
Compare
RDBMS:
int
int
int
int
int
int
int
int
str
str
str
str
str
str
str
str
date
date
date
date
date
date
date
date
General List Processing Languages:
int
str
int
date
date
str
int
str
XQuery:
int
str
xml
date
xml
str
int
str
Copyright 2008 Dan McCreary & Associates

6. FLOWR Expressions on Sequences
for $item in $sequence
let $tmp := $item/path
order by $tmp
where $tmp = ' x '
return
$tmp
Copyright 2008 Dan McCreary & Associates

7. Copyright 2008 Dan McCreary & Associates
Sequences of XML items
sequence
XQuery is based on considering each group of XML documents
as a sequence of items
A sequences is of type item()*
Copyright 2008 Dan McCreary & Associates

8. Copyright 2008 Dan McCreary & Associates
10 Sequence Functions
count
distinct-values
index-of
insert-before
last
position
remove
reverse
subsequence
unordered
Copyright 2008 Dan McCreary & Associates

9. Copyright 2008 Dan McCreary & Associates
Arguments
count($seq as item()*)
distinct-values($seq as item()*)
index-of ($seq as anyAtomicType()*, $targetanyAtomicType())
insert-before($seq as item()*, $position as int, $inserts as item()*)
last ($seq as item()*)
position() as int
remove ($seq as item()*, $position as int)
reverse ($seq as item()*)
subsequence ($seq as item()*, $start as int, $num as int)
unordered
Copyright 2008 Dan McCreary & Associates

10. Copyright 2008 Dan McCreary & Associates
Exercises
Create a sample sequences using letters
Let $input := (‘a’, ‘b’, ‘c’)
Create a simple XQuery to demonstrate all of the 10 operations on a sequence.
Copyright 2008 Dan McCreary & Associates

11. Copyright 2008 Dan McCreary & Associates
Thank You!
Please contact me for more information:
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Dan McCreary, President
Dan McCreary & Associates
Metadata Strategy Development
(952)
Copyright 2008 Dan McCreary & Associates