Web-Base Management Systems

1
Web-Base Management Systems

• Aaron Brown and David Oppenheimer
• CS294-7
• February 11, 1999

2
Introduction

• Online data is stored in both databases
  (relational) and web sites (hypertext)
• Need single framework to manage both types of
  data and present integrated views
• Solution Web Base Management Systems (WBMSs)
• 2 challenges
• 1) querying and extracting structure from
  semi-structured web data, transforming it, and
  presenting custom views
• 2) mapping structured database data to the web
  (adding navigational access paths, redundancy,
  ...)
• To address these challenges, we need a data model
  that maps between relational and hypertextual
  models

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ARANEUS Data Models
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ARANEUS Data Model

• ADM Logical data model for web hypertexts
• Based on page schemes and navigational access
  paths
• Page scheme logical structure shared by a set
  of pages
• Like a class
• Web page instance of page scheme
• Like an object with identifier (URL)
  attributes

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ADM Example Fragment
6
Adding Structure to HTML
EDITOR
ULIXES
Relational
ADM
HTML
PENELOPE
ER NCM
Structure
Navigational access
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EDITOR Structuring HTML

• EDITOR starts with an existing ADM scheme
• Generated by inspection of web site
• EDITOR maps web page text to attributes of an ADM
  page scheme
• Wrapping a web page
• Imposes structure on web pages
• EDITOR uses a procedural language to guide the
  wrapping process
• Each page seen as object with extraction methods
• One method for each attribute of page
• Method accesses pages HTML source, extracts
  value of corresponding attribute

8
Querying ADM-Structured Hypertext
EDITOR
ULIXES
Relational
ADM
HTML
PENELOPE
ER NCM
Structure
Navigational access
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ULIXES A Navigational Query Lang.

• Language for defining relational views over
  hypertext that follows an ADM scheme
• Based on navigational expressions (path
  expressions)
• DEFINE TABLE statement creates relational views
  based on page schemes
• local materialized view (tuples) or
• virtual view
• user can then pose SQL queries across multiple
  views
• optimizer chooses optimal navigation path through
  site to satisfy query
• fetches hypertext pages and extracts attributes
  via EDITOR wrappers
• cost metric is number of HTML page fetches

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ULIXES Example

• DEFINE TABLE VLDBPapers (Authors, Title,
  Reference)
• AS AuthorSearchPage.NameForm.Submit -gt
  AuthorPage.WorkList
• IN DBLPScheme
• USING AuthorPage.WorkList.Authors,
  AuthorPage.WorkList.Title, AuthorPage.WorkLi
  st.Reference
• WHERE AuthorSearchPage.NameForm.Name
  Leonardo Da Vinci AuthorPage.WorkList.Refer
  ence LIKE VLDB

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Generating ADM from existing DB
EDITOR
ULIXES
Relational
ADM
HTML
PENELOPE
ER NCM
Structure
Navigational access
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The ARANEUS Design Methodology
Database Conceptual Design (ER)
Hypertext Conceptual Design (NCM)
Database Logical Design (relational)
Hypertext Logical Design (ADM)
DB Mapping (PENELOPE) Page Design (HTML)
Web Site Generation
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Database Conceptual Model

• Starting point for database design
• Conceptual description of a domain
• Represents essential properties of data
  abstractly
• Entity-Relationship Model
• Based on entities and relationships among
  entities
• Rectangles entity sets
• Associated attributes are connected with lines
• Diamonds relationship sets
• Lines connect entity sets via relationship sets

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ER Example
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Hypertext Conceptual Design

• ER not suitable for modeling hypertext
• no directed paths (links)
• hypertext access paths not modeled (web page
  hierarchies)
• no way to group related entities into a singe
  macroentity
• Navigational Conceptual Model (NCM) describes
  these conceptual properties of hypertext
• macroentities (groups of related ER entites)
  model hypertext nodes
• associated with simple (atomic) or complex
  (structured) attributes, either mono- or
  multi-valued
• directed relationships model links (may be
  bidirectional)
• union nodes model link targets that can be of
  different types
• aggregations model hierarchical access paths

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Mapping ER to NCM Example
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Mapping NCM to ADM

• 1) macroentity -gt one or more pages
  single-valued attribute -gt ADM simple attribute
  multi-valued attribute -gt ADM list
• 2) directed relationship -gt link to another page
  scheme
• anchor a descriptive key of target macroentity
• reference URL of target page scheme
• 3) aggregation node -gt ADM unique page scheme
• unique page scheme page scheme with only one
  instance
• 4) long lists -gt forms
• list items retrieved through program running on
  server

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Mapping NCM to ADM Example
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The ARANEUS Design Methodology
Database Conceptual Design (ER)
Hypertext Conceptual Design (NCM)
Database Logical Design (relational)
Hypertext Logical Design (ADM)
DB Mapping (PENELOPE) Page Design (HTML)
Web Site Generation
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Generating web site from ADM DB
EDITOR
ULIXES
Relational
ADM
HTML
PENELOPE
ER NCM
Structure
Navigational access
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Hypertext Views of DB Data

• Given a database and an ADM scheme for it
• database may be local
• derived from design methodology
• uses derived ADM scheme
• composed from one or more remote sites
• derived from integrated relational view produced
  by one or more ULIXES queries
• uses new ADM scheme concocted to match integrated
  view
• PENELOPE language used to integrate ADM and DB in
  a generated hypertext
• PENELOPE description ADM augmented with URLs
  and references to database fields

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PENELOPE Description

• Query reorganize (Da Vincis VLDB) papers based
  on year

DEFINE PAGE YearPageAS URL URL(ltYeargt) Year
TEXTltYeargt WorkList LIST OF (Authors TEXT
ltAuthorsgt Title TEXT ltTitlegt
Reference TEXT ltReferencegt ToRefPage LINK
TO ConferencePage UNION JournalPage
ltToRefPagegt) FROM DaVinciPapers DEFINE PAGE
DaVinciYearsPage UNIQUE AS URL result.html Yea
rList LIST OF (Year TEXT ltYeargt
ToYearPageLINK TO YearPage (URL(ltYeargt)))
FROM DaVinciPapers
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Derived Hypertext View
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Resulting Web Pages
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Retrospective

• Exceptions during wrapping
• Logically homogenous pages may be physically
  heterogeneous
• Different ways of laying out the same information
• Errors masked by browsers
• ULIXES syntax is difficult for beginners
• Alternatives
• Fill out forms corresponding to pre-determined
  ULIXES queries
• Developed POLYPHEMUS query interface
• User selects path for query by clicking on
  graphical representation of ADM page schemes
• Push vs. Pull
• Either supported hybrid model preferred
• Dealing with updates
• each DB update generates a mixed transaction that
  updates both the DB and any pushed (static) HTML
  pages
• Managing internal sites
• PENELOPE-generated HTML includes description of
  page scheme and tags attributes
• Like XML but uses HTML comments

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Conclusion

• ARANEUS provides database-like functionality for
  mixed web/relational DB data
• More to be filled in later...