Models and languages for semistructured data

1
Models and languages forsemistructured data

• Bridging documents and databases

2
Lectures

• 1. Introduction to data models
• 2. Query languages for relational databases
• 3. Models and query languages for object
  databases
• 4. Models and query languages for semistructured
  data, XML
• 5. Embedded query languages
• 6. Guest lecture on Object Role Modelling

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Why do we like types?

• Types facilitate understanding
• Types enable compact representations
• Types enable query optimisation
• Types facilitate consistency enforcement

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Background assumptions fortyped data

• Data stable over time
• Organisational body to control data
• Exercise Give an example of a context where
  these assumptions do not hold

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Semistructured data
Semistructured data is schemaless and self
describing The data and the description of the
data are integrated
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An example
name first John, last Smith, tel
112233, email john_at_123.edu
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Another example
person o1name Eva, age 40, child
o2, person o2name Abel, age 20
An object identifier, such as o1, before a
structure, binds the object identifier to the
identity of that structure. The object identifier
can then be used to refer to the structure.
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Terminology

• The following is an ssd-expression
• o1name Eva, age 40, child o2

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A database
author
Crick
DNA spiral
author
n1
Wallace
1956
paper
title
date
Origin
1848
Darwin
author
biblio
book
n2
db
title
date
book
Kapital
1860
Marx
author
.
n3
title
date
10
Path expressions

• A path expression is a sequence of labels
• l1.l2ln
• A path expression results in a set of nodes
• Path properties are specified by regular
  expressions on two levels on the alphabet of
  labels and on the alphabet of characters that
  comprise labels

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A path expression
author
Crick
DNA spiral
biblio.book.author
author
n1
Wallace
1956
paper
title
date
Origin
1848
Darwin
author
biblio
book
n2
db
title
date
book
Kapital
1860
Marx
author
.
n3
title
date
12
A path expression
author
Crick
DNA spiral
biblio.(book l paper).author
author
n1
Wallace
1956
paper
title
date
Origin
1848
Darwin
author
biblio
book
n2
db
title
date
book
Kapital
1860
Marx
author
.
n3
title
date
13
Examples of path expressions

• biblio.book.author - authors of books
• biblio.paper.author - authors of papers
• biblio.(book l paper).author - authors of books
  or papers
• biblio._.author - authors of anything
• biblio._.author - nodes at the ends of paths
  starting with biblio, ending with author, and
  having an arbitrary sequence of labels between

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Example of a label pattern

• ((b l B)ook l (a l A)uthor) (s)? - book, Book,
  author, Author, books, Books, authors, Authors

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An exercise

• biblio._.author.(s l Section)
• Which ones of the following paths match the path
  expression above?
• 1. Biblio.author.Section
• 2. Biblio.cat.rat.hat.author.section
• 3. Biblio.author
• 4. Biblio.cat.author.section.Section

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A simple query

• Select author X
• from biblio.book.author X
• Result
• author Darwin, author Marx

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A query with a condition

• select row X
• from biblio._ X
• where Crick in X.author
• Result
• row author Crick,
• author Wallace,
• date 1956,
• title The spiral DNA,

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Two exercises

• select row title Y, date Z
• from biblio.paper X, X.title Y, X.date Z
• select row author Y, date Z
• from biblio.book X, X.author Y, X.date Z

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A database
select row title Y, date Z from biblio.paper
X, X.title Y, X.date Z
author
Crick
DNA spiral
author
n1
Wallace
1956
paper
title
date
Origin
1848
Darwin
author
biblio
book
n2
db
title
date
book
Kapital
1860
Marx
author
.
n3
title
date
20
A database
author
Crick
DNA spiral
author
n1
Wallace
1956
paper
title
date
Origin
1848
Darwin
author
biblio
book
n2
db
title
date
book
Kapital
1860
Marx
author
.
n3
title
date
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Nested queries

• select row (select author Y
• from X.author Y)
• from biblio.book X

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Three exercises

• Which authors have written a book or a paper in
  1992?
• Which authors have written a book together with
  Jones?
• Which authors have written both a book and a
  paper?

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Expressing relations
r1
r2
a b c
b d e
1 2 3
1 1 3
3 2 2
3 4 2
4 3 1
2 3 1
r1 row a 1, b2, c2, row a
1, b2, c2, row a 1, b2, c2 ,
r2 row b 1, d2, e2, row b
1, d2, e2, row b 1, d2, e2
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Expressing relational joins

• select a A, d D
• from r1.row X
• r2.row Y
• X.a A, X.b B, Y.b B, Y.d D
• where B B

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Label variables
Label variable

• select L X
• from biblio._.L X
• where matches(.Shakespeare., X)

Macbeth
1622
Shakespeare
author
biblio
book
n2
db
title
date
book
Best of Shakespeare
1992
Smith
author
.
n3
title
date
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Label variables

• select L X
• from biblio._.L X
• where matches(.Shakespeare., X)
• author Shakespeare,
• title Best of Shakespeare

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Turning labels into data

• select publ type L, author A
• from biblio.L X, X.author A

publ type paper, author Crick, publ
type paper, author Wallace, publ type
book, author Darwin
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An exercise

• List all publications in 1992, their types, and
  titles.

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Basic XML syntax

• XML is a textual representation of data
• An element is a text bounded by tags
• ltnamegt John lt/namegt

ltnamegt lt/namegt can be abbreviated as ltname/gt
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Basic XML syntax

• Elements may contain subelements
• ltpersongt
• ltnamegt John lt/namegt
• lttelgt 112233 lt/telgt
• ltemailgt john_at_123.edu lt/emailgt
• lt/persongt

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XML attributes

• An attribute is defined by a name-value pair
  within a tag
• ltprice currency dollargt 500 lt/pricegt
• ltlength unit cmgt 25 lt/lengthgt

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XML attributes and elements

• ltproductgt
• ltnamegt widget lt/namegt
• ltpricegt 10 lt/pricegt
• lt/productgt
• ltproduct price 10gt
• ltnamegt widget lt/namegt
• lt/productgt
• ltproduct name widget price 10/gt

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XML and ssd-expressions

• ltpersongt
• ltnamegt John lt/namegt
• lttelgt 112233 lt/telgt
• ltemailgt john_at_123.edu lt/emailgt
• lt/persongt

person name John, tel 112233, email
john_at_123.edu
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XML references

• ltperson id p1gt
• ltnamegt John lt/namegt
• lttelgt 112233 lt/telgt
• lt/persongt
• ltperson id p2gt
• ltnamegt Peter lt/namegt
• lttelgt 998877 lt/telgt
• ltboss idref p1/gt
• lt/persongt

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Document Type Definitions

• lt!DOCTYPE db
• lt!ELEMENT db (person)gt
• lt!ELEMENT person (name, age, email)gt
• lt!ELEMENT name (PCDATA)gt
• lt!ELEMENT age (PCDATA)gt
• lt!ELEMENT email (PCDATA)gt
• gt

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An exercise on DTDs as schemas

• ltdbgt ltr1gt ltagt a1 lt/agt ltbgt b1 lt/bgt lt/r1gt
• ltr1gt ltagt a2 lt/agt ltbgt b2 lt/bgt lt/r1gt
• ltr2gt ltcgt a1 lt/cgt ltdgt b1 lt/dgt lt/r1gt
• ltr2gt ltcgt c2 lt/cgt ltdgt d2 lt/dgt lt/r1gt
• ltr3gt ltagt a1 lt/agt ltcgt b1 lt/cgt lt/r1gt
• lt/dbgt
• Write down a DTD for the data above!

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Attributes in DTDs

• ltproductgt
• ltname language Swedish department musicgt
• trumpet lt/namegt
• ltprice currency dollargt 500 lt/pricegt
• ltlength unit cmgt 25 lt/lengthgt
• lt/productgt

lt!ATTLIST name language CDATA REQUIRED
department CDATA IMPLIEDgt lt!ATTLIST price
currency CDATA REQUIREDgt lt!ATTLIST length unit
CDATA REQUIREDgt
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Reference attributes in DTDs

• lt!DOCTYPE people
• lt!ELEMENT people (person)gt
• lt!ELEMENT person (name)gt
• lt!ELEMENT name (PCDATA)gt
• lt!ATTLIST person id ID REQUIRED
• boss IDREF REQUIRED
• friends IDREFS IMPLIEDgt
• gt

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An exercise

• ltpeoplegt
• ltpersongt id sven boss ollegt
• ltnamegt Sven Svensson lt/namegt
• lt/persongt
• ltpersongt id olle friends nils evagt
• ltnamegt Olle Olsson lt/namegt
• lt/persongt
• ltpersongt id pelle boss nils evagt
• ltnamegt Per Persson lt/namegt
• lt/persongt
• ltpeoplegt
• Does this XML element conform to the previous
  DTD?

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Limitations of DTDs as schemas

• DTDs impose order
• No base types
• The types of IDREFs cannot be constrained

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XSL - extensible stylesheet language

• ltbibgt ltbookgt lttitlegt t1 lt/titlegt
• ltauthorgt a1 lt/authorgt
• ltauthorgt a2 lt/authorgt
• lt/bookgt
• ltpapergt
• lttitlegt t2 lt/titlegt
• ltauthorgt a3 lt/authorgt
• ltauthorgt a4 lt/authorgt
• lt/papergt
• ltbookgt lttitlegt t3 lt/titlegt
• ltauthorgt a5 lt/authorgt
• ltauthorgt a6 lt/authorgt
• lt/bookgt
• lt/bibgt

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Template rules and XSL patterns

• ltxsl templategt
• ltxsl apply-templates/gt
• lt/xsl templategt
• ltxsl template match bib//titlegt
• ltresultgt
• ltxsl value-of/gt
• lt/resultgt
• lt/xsl templategt

ltresultgt t1 lt/resultgt ltresultgt t2
lt/resultgt ltresultgt t3 lt/resultgt
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Two exercises

• select row title Y, date Z
• from biblio.paper X, X.title Y, X.date Z
• row title The spiral DNA,
• date 1956,
• title Origin,
• date 1848,
• title Kapital,
• date 1860
• select row author Y, date Z
• from biblio.book X, X.author Y, X.date Z

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Which authors have written a book or a paper in
1992? select author X from biblio.(book
paper) Y, Y.author X where Y.date 1992
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Which authors have written a book together with
Jones? select author X from biblio.book Y,
Y.author X where Jones in Y.author
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Which authors have written both a book and a
paper? select author A from biblio.book B,
biblio.paper P, B.author A where B.author
P.author select author A1 from biblio.book B,
biblio.paper P, B.author A1, P.author A2 where A1
A2
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List all publications in 1992, their types, and
titles. select publ type L, title T from
biblio.L X, X.title T where X.date 1992
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• lt!DOCTYPE db
• lt!ELEMENT db (r1, r2, r3)gt
• lt!ELEMENT r1 (a, b)gt
• lt!ELEMENT r2 (c, d)gt
• lt!ELEMENT r3 (a, c)gt
• lt!ELEMENT a (PCDATA)gt
• lt!ELEMENT b (PCDATA)gt
• lt!ELEMENT c (PCDATA)gt
• lt!ELEMENT d (PCDATA)gt
• gt
• ltdbgt ltr1gt ltagt a1 lt/agt ltbgt b1 lt/bgt lt/r1gt
• ltr1gt ltagt a2 lt/agt ltbgt b2 lt/bgt lt/r1gt
• ltr2gt ltcgt a1 lt/cgt ltdgt b1 lt/dgt lt/r1gt
• ltr2gt ltcgt c2 lt/cgt ltdgt d2 lt/dgt lt/r1gt
• ltr3gt ltagt a1 lt/agt ltcgt b1 lt/cgt lt/r1gt
• lt/dbgt