WebBase Management Systems Aaron Brown and David Oppenheimer

Web-Base Management Systems Aaron Brown and David Oppenheimer CS 294 -7 February 11, 1999 Slide 1

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 Slide 2

ARANEUS Data Models Relational ADM HTML Structure Navigational access Slide 3

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 Slide 4

ADM Example Fragment Slide 5

Adding Structure to HTML Relational ADM HTML Structure Navigational access Slide 6

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 page’s HTML source, extracts value of corresponding attribute Slide 7

Querying ADM-Structured Hypertext Relational ADM HTML Structure Navigational access Slide 8

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 Slide 9

ULIXES Example DEFINE TABLE VLDBPapers (Authors, Title, Reference) AS Author. Search. Page. Name. Form. Submit -> Author. Page. Work. List IN DBLPScheme USING Author. Page. Work. List. Authors, Author. Page. Work. List. Title, Author. Page. Work. List. Reference WHERE Author. Search. Page. Name. Form. Name = ‘Leonardo Da Vinci’ Author. Page. Work. List. Reference LIKE ‘%VLDB%’ Slide 10

Generating ADM from existing DB Relational ADM HTML Structure Navigational access Slide 11

The ARANEUS Design Methodology Database Conceptual Design (ER) Database Logical Design (relational) Hypertext Conceptual Design (NCM) Hypertext Logical Design (ADM) DB Mapping (PENELOPE) + Page Design (HTML) Web Site Generation Slide 12

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 Slide 13

ER Example Slide 14

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 Slide 15

Mapping ER to NCM: Example Department Room# Room General Title Speaker Date People Seminar Name Phone Professor 1: N SPlace 1: 1 1: N Responsible ER Model Education Research 1: 1 Seminar Room# Title Speaker Date Responsible 1: 1 Professor Name Phone NCM Model Slide 16

Mapping NCM to ADM 1) macroentity -> one or more pages single-valued attribute -> ADM simple attribute multi-valued attribute -> ADM list 2) directed relationship -> link to another page scheme – anchor = a descriptive key of target macroentity – reference = URL of target page scheme 3) aggregation node -> ADM “unique” page scheme – unique page scheme = page scheme with only one instance 4) long lists -> forms – list items retrieved through program running on server Slide 17

Mapping NCM to ADM: Example Slide 18

The ARANEUS Design Methodology Database Conceptual Design (ER) Database Logical Design (relational) Hypertext Conceptual Design (NCM) Hypertext Logical Design (ADM) DB Mapping (PENELOPE) + Page Design (HTML) Web Site Generation Slide 19

Generating web site from ADM + DB Relational ADM HTML Structure Navigational access Slide 20

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 URL’s and references to database fields Slide 21

PENELOPE Description • Query: reorganize (Da Vinci’s VLDB) papers based on year DEFINE PAGE Year. Page AS URL Year: Work. List: FROM Da. Vinci. Papers URL(<Year>); TEXT<Year>; LIST OF (Authors: Title: Reference: To. Ref. Page: TEXT <Authors>; TEXT <Title>; TEXT <Reference>; LINK TO Conference. Page UNION Journal. Page <To. Ref. Page>); DEFINE PAGE Da. Vinci. Years. Page UNIQUE AS URL ‘result. html’; Year. List: LIST OF (Year: TEXT <Year>; To. Year. Page: LINK TO Year. Page (URL(<Year>))); FROM Da. Vinci. Papers Slide 22

Derived Hypertext View Slide 23

Resulting Web Pages Slide 24

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 Slide 25

Conclusion • ARANEUS provides database-like functionality for mixed web/relational DB data • More to be filled in later. . . Relational ADM HTML Slide 26