1. Lecture 15: Midterm Review
Friday, October 31, 2003

2. XML Storage Most often the XML data is small
E.g. a SOAP message
Parsed directly into the application (DOM API)
Sometimes XML data is large
need to store/process it in a database
The XML storage problem:
How do we choose the schema of the database ?

3. XML Storage Three solutions: Schema derived from DTD
Storing XML as a graph: “Edge relation”
Store it as a BLOB
Simple, boring, inefficient
Won’t discuss in class

4. Designing a Schema from DTD
Design a relational schema for:
<!DOCTYPE company [
<!ELEMENT company ((person|product)*)>
<!ELEMENT person (ssn, name, office?, phone*)>
<!ELEMENT ssn (#PCDATA)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT office (#PCDATA)>
<!ELEMENT phone (#PCDATA)>
<!ELEMENT product (pid, name, ((price,availability)|description))>
<!ELEMENT pid (#PCDATA)>
<!ELEMENT description (#PCDATA)>
]>

5. Designing a Schema from DTD
First, construct the DTD graph:
company *
We ignore the order *
person
product *
ssn
name
office
phone
pid
price
avail.
descr.

6. Designing a Schema from DTD
Next, design the relational schema, using common sense.
company * *
person
product *
ssn
name
office
phone
pid
price
avail.
descr.
Person(ssn, name, office) Phone(ssn, phone) Product(pid, name, price, avail., descr.)
Which attributes may be NULL ? (Look at the DTD)

7. Designing a Schema from DTD
What happens to queries:
FOR $x IN /company/product[description]
RETURN <answer> { $x/name, $x/description } </answer>
SELECT Product.name, Product.description
FROM Product
WHERE Product.description IS NOT NULL

8. Storing XML as a Graph Sometimes we don’t have a DTD:
How can we store the XML data ?
Every XML instance is a tree
Store the edges in an Edge table
Store the #PCDATA in a Value table

9. Can be ANY XML data (don’t know DTD)
Storing XML as a Graph
Can be ANY XML data (don’t know DTD) db
book
publisher
title
author
state
“Complete
Guide
to DB2”
“Chamberlin”
“Transaction
Processing”
“Bernstein”
“Newcomer”
“Morgan
Kaufman”
“CA” 1 2 3 4 5 6 7 8 9 10 11
Edge
Source
Tag
Dest db 1
book 2
title 3
author 4 5 6 7
. . .
Value
Source
Val 3
Complete guide . . . 4
Chamberlin 6
. . .

10. Storing XML as a Graph FOR $x IN /db/book[author/text()=“Chamberlin”]
What happens to queries:
FOR $x IN /db/book[author/text()=“Chamberlin”]
RETURN $x/title
xdb
xbook
xauthor
xtitle
vauthor
vtitle db
book
author
title
“Chamberlin”
Return value

11. Storing XML as a Graph What happens to queries: A 6-way join !!!
SELECT vtitle.value
FROM Edge xdb, Edge xbook, Edge xauthor, Edge xtitle, Value vauthor, Value vtitle
WHERE xdb.source = and xdb.tag = ‘db’ and xdb.dest = xbook.source and xbook.tag = ‘book’ and xbook.dest = xauthor.source and xauthor.tag = ‘author’ and xbook.dest = xtitle.source and xtitle.tag = ‘title’ and xauthor.dest = vauthor.source and vauthor.value = ‘Chamberlin” and xtitle.dest = vtitle.source

12. Storing XML as a Graph Edge relation summary:
Same relational schema for every XML document:
Edge(Source, Tag, Dest)
Value(Source, Val)
Generic: works for every XML instance
But inefficient:
Repeat tags multiple times
Need many joins to reconstruct data

13. Other XML Topics Name spaces XML API: XML languages: XML Schema
DOM = “Document Object Model”
XML languages:
XSLT
XML Schema
Xlink, XPointer
SOAP
Available from
(but don’t spend rest of your life
reading those standards !)

14. Research on XML Data Management at UW
Processing:
Query languages (XML-QL, a precursor of XQuery)
Tukwila
XML updates
XML publishing/storage
SilkRoute: silkroute.sourceforge.net
STORED
XML tools
XML Compressor: Xmill
XML Toolkit (xsort, xagg, xgrep, xtransf, etc): xmltk.sourceforge.net
Theory:
Typechecking
Xpath, Xquery containment

15. The Midterm
Four questions:
SQL
E/R
Schema design (BCNF/3NF)
XML

16. The Midterm Open book exam (books,/notebooks,/lectures) No retakes
But no computers
No retakes
Your score: Max(midterm-score,100 – 1.2(100 – final-score)
No retakes on final: you *must* take it on Dec. 12

17. 1. SQL Selection/project/join Understand well duplicates
Aggregate queries
avoid nested queries when a GROUP BY suffices
Nested queries
More difficult: ANY, ALL, NOT IN
Updates, table creations, views

18. 2. E/R Diagrams One/many v.s. many/many relationships Inheritance
Translation to relations
Remember: no table for one/many !

19. 3. Schema Design What does AB  CD mean ? Compute {AB}+
Compute all keys
Decompose in BCNF or 3NF

20. 4. XML XML: XPath XQuery Basic principles in publishing/storing data
Basic syntax: elements + attributes
DTDs: elements only
The tree model
Canonical XML view of a relation (<row>...)
XPath
XQuery
Basic principles in publishing/storing data

21. Final Thoughts Open book Some question(s) may be hard(er)
But read the book before the exam
Some question(s) may be hard(er)
Answer first the questions that are easier
The answers should not be very complex

22. Exercises ABC, CD, DB, DE Decompose in BCNF
General strategy: find X s.t.: X  X+  all attributes

23. BCNF Try AB+ = ABCDE nope… Try C+ = CDBE yep… decompose CDBE, CA
ABC, CD, DB, DE
BCNF
Try AB+ = ABCDE nope…
Try C+ = CDBE yep… decompose CDBE, CA
Continue in CDBE: try D+ = DBE yep… decompose DBE, DC
Continue in DBE: try D+ = DE yep… decompose DE, DB
Answer: CA, DC, DE, DB
Notice: AB is a key, but A and B are separated. Cleary 3NF differs

24. 3NF ABC, CD, DB, DE Minimal keys: AB, AC, AD
Try C+ = CDBE yes, BUT: D,B part of keys so decompose on C E only: CE, CABD
Continue in CABD
Try A+ = A nope… Try B+ = B nope… Try AB+ = ABCD nope… Try C+ = CDB yes, but B, D part of keys Try D+ = DB again B part of a key Try others… nope.
Answer: CE, CABD. Notice: DE, DABC also OK