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XML und Data Management
- Introduction -
Hachim Haddouti
Al Akhawayn University
SSE
[email protected]
http://mail.alakhawayn.ma/~H.Haddouti
Table of Conetnt
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Intro
Motivation
Semi structured data
Why do we need semistructured data?
What is semistructured data?
Hachim Haddouti
Motivation
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Some data really is unstructured
Examples:
– World Wide Web
– Data exchange formats
– Data Integration
Hachim Haddouti
Motivation - Web
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Why do we want to treat the Web as a database?
– Maintain integrity
– Query based on structure (as opposed to content)
– Introduce some “organization”
However, Web has no structure, refer to it as enormous graph
Some people claim database research community missed the
boat when it comes to the World Wide Web
Hachim Haddouti
Motivation – Data Formats
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Much (most?) of the world’s data is in data formats
– Formats defined for interchange and archiving of data
Formats vary in generality
– ASN.1, EDI quite general
– Scientific data formats tend to be “fixed schema”
Textual representation given by data formats not
immediately translatable into standard relation/objectoriented representation
Hachim Haddouti
ASN.1
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Abstract Syntax Notation number One (ASN.1)
– International standard that aims at specifying data used
in communication protocols
– e.g., format for transporting data between two layers of
a network operating system
Now used for storing bibliographic and genetic data
Want more, go to www.asn1.elibel.tm.fr/en/introduction/
Hachim Haddouti
Sample ASN.1 Module
Module-order DEFINITIONS AUTOMATIC TAGS ::=
BEGIN
Order ::= SEQUENCE {
header
Order-header,
items
SEQUENCE OF Order-line }
Order-header ::= SEQUENCE {
reference
NumericString (SIZE (12)),
date
NumericString (SIZE (8)) -- MMDDYYYY --,
client
Client,
payment
Payment-method }
Client ::= SEQUENCE {
name
PrintableString (SIZE (1..20)),
street
PrintableString (SIZE (1..50)) OPTIONAL,
postcode
NumericString (SIZE (5)),
town
PrintableString (SIZE (1..30)),
country
PrintableString (SIZE (1..20)) DEFAULT "France" }
Payment-method ::= CHOICE {
check
NumericString (SIZE (15)),
credit-card
Credit-card,
cash
NULL }
Credit-card ::= SEQUENCE {
type
Card-type,
number
NumericString (SIZE (20)),
expiry-date
NumericString (SIZE (6)) -- MMYYYY -- }
Card-type ::= ENUMERATED {cb(0), visa(1), eurocard(2), diners(3), american-express(4)}
-- etc
END
Hachim Haddouti
EDI
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EDI = Electronic Data Interchange
Provides a collection of standard message formats and element
dictionary to support exchange of data via any electronic
messaging service
Hachim Haddouti
Sample EDI Invoice File
ISA~00~ ~00~ ~ZZ~YOUR COMM-ID ~14~SLKP COMM-ID
~000227~1053~U~00401~000000012~0~P~>
GS~IN~YOUR COMM-ID~SLKP COMM-ID~20000227~1053~3~X~004010
ST~810~0001
BIG~19991118~001001~19990926~11441~~~DR
N1~RE~REMIT COMPANY, INC~92~002377703
N3~P.O. BOX 111
N4~ANYTOWN~NC~27106
N1~ST~SARA LEE FOOTWEAR
N3~SHIPPING STREET
N4~OUR TOWN~PA~17855
N1~BT~SARA LEE FOOTWEAR~92~10
N3~470 W. HANES MILL RD
N4~WINSTON SALEM~NC~27105
ITD~05~3~~~~~60
DTM~011~19991118
IT1~0001~1470~YD~2~~BP~BUYERPART
PID~F~~~~Square Rubber Hose
TDS~294000
ISS~1470~YD
CTT~1~1470
SE~19~0001
GE~1~3
Hachim Haddouti
IEA~1~000000012
Motivation - Browsing
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To query database, one needs to understand schema
Schemas may be hard to understand, users may want to start by
querying data with little or no knowledge of schema
– Where in database is string “Casablanca”?
– Are there integers in database greater than 216?
– What objects in db have attribute name that starts with “act”?
Some extensions to relational query languages have been proposed for
such queries
Hachim Haddouti
Motivation – Integration of
Heterogeneous Data
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With the growing amount of information distributed in
multiple sources, comes an increased need for tools
and algorithms to provide integrated, unified interface
to information
Information integration is another application which
calls for flexible, dynamic, self-describing data model
Hachim Haddouti
Content from Multiple Sources
…and, if possible, is a
preferred supplier
3rd party
content
Who offers the
cheapest 10+ Nm motor,
matching with my XYZ123 drive,
operating <12V, available
within 2 days ?
Product
Catalog
Pricing
Supplier
Hachim Haddouti
Delivery
Supplier
Information
Product
Catalog
ERP
(P + D)
Supplier
Supply Chain Management
Expected
Supplies
Outstanding
Customer
Orders
Sales
Pipeline
Info
Product
Returns
Flaky Inc.’s shipment is coming two days later
than needed… Given the state of our inventory, expected
orders, identity (and value) of customers, and pricing and
delivery options, how can we satisfy our best customer at the
price we promised them?
Shipments to
ACME
Flaky
Inc.
Hachim Haddouti
Shipments to
Pricing &
ACME
Delivery
Credible Inc.
… Or Viewed in Different Terms
Personal
Databases
“Heterogeneities are everywhere”
World
Wide
Web
Scientific Databases
Digital Libraries
• Different interfaces
• Different data representations
• Duplicate and inconsistent information
Hachim Haddouti
14
Integrated View of Heterogeneous Data
Integration System
World
Wide
Web
•
•
•
Digital Libraries
Scientific Databases
Personal
Databases
Collects and combines information
Provides integrated view, uniform user interface
Supports sharing
Hachim Haddouti
15
World of Data Access and
Integration Servers
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Provide to the eBusiness application unified access to the data
sources
Data of multiple sources appear as if they come from one
(potentially virtual) database
as ubiquitous as application servers
Driven by initiatives in
– Customer Relationship Management
– Supply Chain Management
– eCommerce and eContent
– Business Intelligence and Warehousing
Hachim Haddouti
Most-Generic Integration System
Architecture
Clients
Integrator
...
Wrapper
Wrapper
Wrapper
...
Information
Source
Hachim Haddouti
Information
Source
Information
Source
How Do We Represent Data in the
Integration System?
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Relational Data Model
– Set of rows and columns
– Fixed set of simple data types
Data cube
– Specialized warehouse management system
– Uses a single, multi-dimensional relation as model
Neither!! Both models are too rigid to accommodate
heterogeneous data from multiple sources
Hachim Haddouti
Bottom Line
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We need a bridge between the repositories where the data
resides (e.g., data warehouse, transactional databases) and
where it is used (Web interface, business application)
Data model that allows for the exchange of data with
structure
Relaxes the strictures of existing, highly structured
database systems
Hachim Haddouti
New Data Model:
Semistructured Data Model
Hachim Haddouti
Semistructured Data: Particularities (1)
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Structure is irregular – data heterogeneities
– Pieces of data missing
– Extra information is recorded (annotations)
– Type variations (Dollars/Euros – Address)
Structure may be implicit
– Often in files: text + grammar (e.g., SGML)
• Need to parse – structuring may be hidden
Hachim Haddouti
Semistructured Data: Particularities (2)
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Structure may be partial
– Parts of data lack structure (e.g., images)
– Some data may yield little structure (e.g., plain text)
Types are only indicative
– Unlike databases, some sources may not have strict typing
policy
Hachim Haddouti
Semistructured Data: Particularities (3)
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A-priori schema vs. a-posteriori:
– Database: Fix schema, then populate
– Web: design a lot of Web pages, then define schema to
facilitate access
Schema is large
Schema often ignored in queries
– IR queries and browsing
Hachim Haddouti
Semistructured Data: Particularities (4)
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Schema is rapidly evolving
Data element type is eclectic
– Structure of a piece of information may depend on point of
view
– e.g., Person object contains, name, address, phone as
strings and picture as gif file
Hachim Haddouti
Example
{name: “Alan”, tel: 2157786, email: “[email protected]”}
{name: {first: “Alan”, last: “Black”},
tel: 2157786,
email: “[email protected]”
}
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Different from usual tuples in that we allow duplicates:
{name: “Alan”, tel: 2157786, tel: 2159989, email: “[email protected]”}
Hachim Haddouti
Graph Representation
node
name
email
name
tel
“Alan”
2157786 “[email protected]”
Hachim Haddouti
edges
tel
email
2157786 “[email protected]”
first
last
“Alan”
“Black”
Example
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Possible to describe sets of tuples:
{person:
{name: “Alan”, tel: 2157786, email: “[email protected]”},
person:
{name: “Sara”, tel: 2344381, email: “[email protected]”},
person:
{name: “Fred”, tel: 7767546, email: “[email protected]”}
}
Hachim Haddouti
Example – Variations in Structure
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Possible to describe sets of heterogeneous tuples:
{person:
{name: “Alan”, phone: 2157786, email: “[email protected]”},
person:
{name: {first: “Sara”, last: “Green”},
tel: 2344381,
email: [email protected]
},
person:
{name: “Fred”, tel: 7767546, height: 6’4”}
}
Hachim Haddouti
Base Types
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Numbers: (1234, 45, 4532, …)
Strings: (“Alan”, “ssdrf”, “[email protected]”, …)
Labels: (name, email, …)
Distinguishable by syntax
Other types such as gif, date, wav, etc. can be added as
needed
– Each value has a tag that indicates its type and possibly
an encoding
– Most data formats have their own tagging
Hachim Haddouti
Representing Relational Databases
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Relational schema r1(a,b,c) and r2(c,d)
– r1 and r2 are relations,
– a, b, c, d column names
Instance is some data that conforms to this specification
– Usually depicted as rows in table
Hachim Haddouti
Pictorially
r1
a
b
c
r2
c
d
a1 b1 c1
c2 d1
a2 b2 c2
c3 d2
a3 b3 c3
c4 d3
Hachim Haddouti
Self-describing Approach
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Using our new model and syntax, we can describe the whole database formally
as: {r1: i1, r2: i2}, where i1 and i2 are sets of rows
{r1: {row: {a: a1, b: b1, c: c1},
row: {a: a2, b: b2, c: c2},
row: {a: a3, b: b3, c: c3}
},
r2: {row: {c: c2, d: d2},
{row: {c: c3, d: d3},
{row: {c: c4, d: d4}
}
}
Hachim Haddouti
Other Representations
r2
r1
row
row
a
a1
b
b1
row
row
row
c
a
c1 a2
b
b2
c
a
c2 a3
Hachim Haddouti
b
b3
row
c
c
c3
c2
d
d2
c
c3
d
d3
c
c4
d
d4
Other Representations
r1
a
a1
b
b1
c
a
c1 a2
r1
r1
b
b2
c
a
c2 a3
Hachim Haddouti
b
b3
r2
c
c
c3
c2
r2
d
d2
r2
c
c3
d
d3
c
c4
d
d4
The Object Exchange Model
(OEM)
 Common model for heterogeneous information
exchange, “schema-less”
 Each object:
OID

Label
Type
Value
OID = unique identifier or NULL
 Label = character string descriptor
 Type = atomic data type or set
 Value = atomic value or set of object references
 “Help pages” for labels
 Two
query languages
Hachim Haddouti
OEM
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Provides:
– Flexibility: rigid domain models not needed for those
software components which do not require one
– Extensibility: information servers can use whatever
information is available and can rapidly make its
knowledge available on an experimental basis
– Stability: the structure of the information remains stable
even as new information is added
Removes dependencies on compile-time object definitions
Hachim Haddouti
Representing Semistructured Data
Using OEM
Set Value
Label
Memory
Addresses
<book, {t1, a1}>
t1: <title, “Database and ...”>
a1: <author, “Jeff Ullman”>
Atomic Value
Hachim Haddouti
Representing Semistructured Data
Using OEM
<collection, {b1, a1, ...}>
b1: <book, {t, a}>
t: <title, “Database and ...”>
a: <author, {n, p}>
n: <name, “Jeff Ullman”>
p: <picture, “/gifs/ullman.gif”>
a1: <article, {v, w, x}>
v: <author, “Gio Wiederhold”>
w: <title, “Mediators in the …”>
x: <journal, “IEEE Computer”>
...
Hachim Haddouti
Example: ACeDB
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ACeDB (a C. elegans Database)
Genome database system developed since 1989 primarily by Jean ThierryMieg (CNRS, Montpellier) and Richard Durbin (Sanger Institute)
Provides custom database kernel, with non-standard data model designed
specifically for handling scientific data flexibly
AceDB is used both for managing data within genome projects, and for
making genomic data available to the wider scientific community.
– Popular with biologists for its flexibility and ability to accommodate
missing data
– Underlying data model is quite general
Hachim Haddouti
Sample AceDB Schema
?person name firstname UNIQUE Text
lastname UNIQUE Text
tel Int
- at most one first name
- at most one last name
- several numbers
?book authors ?person
title UNIQUE Text
chapter-headings Int UNIQUE Text
- set of persons
- at most one title
- array of strings
…
Hachim Haddouti
Sample ACeDB Data
&ASmith person name firstname “Alan”
lastname “Smith”
- ASmith is key/OID
&JMiller person name firstname “Janet”
lastname “Miller”
&LH17.23.15 authors &ASmith
&JMiller
title “A Very Very Brief History of Time”
chapter-headings 1 “The Beginning”
chapter-headings 2 “The Middle”
chapter-headings 3 “The End”
…
Hachim Haddouti
Is ACeDB Semistructured?
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Any label other then top identifier can be missing
OID’s provided by user
ACeDB requires schema, but data may be missing, no strong typing (labels instead)
Hachim Haddouti
Proposal for Generic SS Data
Syntax
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Semistructured data expressions: ssd-expressions
– Standard syntax for labels and for atomic values
– Object identifiers start with ampersand, e.g., &123
<ssd-expression>::= <value> | oid<value>|oid
<value>::= atomicvalue | <complexvalue>
<complexvalue>::= {label:<ssd-expression>, … ,
label:<ssd-expression>}
Hachim Haddouti
Example
{person: &o1{name: “Mary”,
age: 45,
child: &o2,
child: &o3
},
person: &o2{name: “John”,
age: 17,
relatives: {mother: &o1,
sister: &o3}
},
person: &o3{name: “Jane”,
country: Canada,
mother: &o1
}
}
Hachim Haddouti
Pictorially (edge-labeled graph)
person
person
person
child
&o1
child
&o2
&o3
mother
name
age
name
name
age
country
relatives
“Mary”
45
“John”
mother
Hachim Haddouti
17
“Jane”
sister
“Canada”
Terminology
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Terminology used to describe semistructured data is that of
basic graph theory
Hachim Haddouti
Basic Graph Theory
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Graph (N,E) set of nodes N and set of edges E
Each edge e is associated with a pair of nodes, source node s(e)
and target node t(e)
Path is a sequence e1, e2, … , ek edges such that t(ei) = s(ei+1), 1
 i  k-1
– Number of edges in path is length
Node r is root for graph (N,E) if there is a path from r to n for every
node in N, n  r
A cycle in a graph is a path between a node and itself
– Graph with no cycles is acyclic
A rooted graph is s tree if there is a unique path from r to n for
every n  N, nr
Hachim Haddouti
Sample Graphs
Directed graph with cycle and no root
Tree
Hachim Haddouti
Summary
Def.: Semistructured data model
Is a syntax for data with no separate syntax for types, i.e.,
data that has no separate schema language or data
definition language.
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Data graph vs ssd-expressions
Our semistructured data model is that of an edge-labeled
graph
– Each edge has a label
Hachim Haddouti