CSE 880. Advanced Database Systems. Semistuctured Data and XML

Transcription

1 CSE 880 Advanced Database Systems Semistuctured Data and XML S. Pramanik 1

2 Semistructured Data 1. Data is self describing with schema embedded to the data itself. 2. Theembeddedschemacanchangewithtimejustlike the data changes with time. 3. More flexible than models with separate schema(e.g., relational model) (embedded structure information can be changed; No need to restructure the whole data set.) 4. Data semantics can be more easily understood directly from the data. (because the structure information is with the data). 5. Less efficient in query formulation and processing than data models with fixed schema. 2

3 Use of Semistructured Data 1. For Documents Modeling. (e.g., chemical data may be represented by semistructured data.) 2. A tool for information integration. ( wrappers can be designed for each different database to translate it into semistructured data). 3. XML is based on semistructured data and is popular for data exchanges on the web. 3

4 XML 1. XML: Extensible Markup Language 2. Semistructured data model proposed as a standard for data exchange on the web. 3. A simplified version of SGML 4. Not only for textual data, can represent any kind of information including images. 4

5 Data Structure of XML 1. An XML document is a labeled, unranked, ordered tree 2. Labeled means that some annotation, the label, is attached to each node. Unranked means that there is no a priori bound on the number of children of a node. Ordered means that there is an order between the children of each node. 3. (a) labelonnodes;canquerybyselectingnodesusing the labels, values at the leaf (XML) (b) Model can be labels on edges: values at the leaf (not XML) 4. ELEMENT nodes are the internal nodes. 5. Text nodes do not have names but have values. 6. ELEMENT nodes have contents and can have attributes. 7. Content can contain complex subtrees while attributes value is atomic. 8. Adocumentisatreewithauniquerootandaunique child of type element, called the root element. 9. An element has an opening tag and a closing tag. 10. Anopeningtagcanhavealistof(name, Value)pairs called attributes: 5

6 1. <element1> content 1 <element2> content 2 </element 2> </element 1> Examples element 1 element node / \ text node content 1 element 2 element node can be nested elements content 2 text node 2. An opening tag with list of attributes((name, Value) pairs): <element1> content 1 <element2 name: john title= smith> content 2 </element 2> <element 1> element 1 element node / \ text node content 1 element 2 element node / / Name:john title:smith content 2 text node 6

7 Serialization of the tree and Semantic Issues 1. serialize it by annotating each data item explicitly with its description (such as name, phone, etc.). 2. serialization converts data into a byte stream that can be easily transmitted and reconstructed at the receiver. 3. Self-describing data wastes space, but gains interoperability, which is crucial in theweb context. entry / / \ name work purpose / \ / \ \ fn ln MSU address like to teach \ Jean Doe city Zip x@cse NewYork Figure: An XML document The document of the above figure can be serialized as follows: <entry><name><fn>jean</fn><ln>doe</ln></name>msu<adress><city> NewYork</city><zip>94235</zip></adress>< >x@cse</ > </job><purpose>like to teach</purpose></entry> or with some beautification as <entry> <name> <fn>jean</fn> <ln>doe</ln> </name> <work> MSU 7

8 <adress> <city>newyork</city> <zip>94235</zip> </adress> </work> <purpose>like to teach</purpose> </entry> 4. In this serialization, the data corresponding to the subtree with root labeled work is represented by a subtree delimited by an opening tag < work > and a closing tag < /work >. 5. This is just a serialization. The conceptual (and mathematical) view of an XML document is that it is a labeled, unranked, ordered tree. 6. XML specifies a syntax and no apriori semantics. So, it specifies the content of a document but not its behavior or how it should be processed. 7. The labels have no predefined meaning unlike in HTML, where, for example, the label href indicates a reference and img an image. 8. Labels will be assigned meaning by applications. element node text node comes here from the beginning of this text. 8

9 XML (highlights) : Summarize 1. MuchlikeHTMLusingNESTED tags,excepttags are user defined. 2. XMLtagsusedformeaningofsubstringswithindocuments. 3. Allows schema: DTD(still being used), XML-schema, XQuery 9

10 An Example of Semistructured Data STAR-MOVIE-DATA star star movie starsin name cf address address mh name city street sw starof title year Carrie Fisher street city street city Mark Hamill Oak B wood Star Wars 1977 Maple H wood Locust Malibu starsin starof 1. Root is the entry point to the data (document). 2. Arcs are labeled here (but label can be with the nodes). Arcs indicate the relationship between the node at the head of the arc and the tail. 3. Leafs have the associated data while non-leafs represent the semantic (application interpreted) of the data in the subtree under the node. 10

11 Example of an XML Document for the Previous Tree 1. <? XML VERSION = "1.0" STANDALONE = "yes"?> <STARS-MOVIE-DATA> <STAR> <NAME> Carrie Fisher</NAME> <ADDRESS><STREET>123 Maple St.</STREET> <CITY>Hollywood</CITY></ADDRESS> <ADDRESS><STREET>5 Locust Ln.</STREET> <CITY>Malibu</CITY></ADDRESS> </STAR> <STAR> <NAME> Mark Hamill</NAME> <ADDRESS><STREET>456 Oak Rd.</STREET> <CITY>Brentwood</CITY></ADDRESS> </STAR> <MOVIE> <TITLE>Star Wars</TITLE> <YEAR>1977</YEAR> </MOVIE> </STARS-MOVIE-DATA> 2. Header line is enclosed by markers <?? > 3. STANDALONE= yes means no DTD used. 4. < STAR MOVIE DATA > is the root element of the XML document. 11

12 Schema for XML Documents 1.XMLdocumentcanbecreatedwithout schema 2. Does not provide constraints. (e.g., no integer type, no key constraint, etc.) 3. DTD: Document Type Definition (Provide some constraints in terms of order in which the tags can occur in a document. ) 4. XML Schema (recently proposed and still evolving more sophisticated schema facilities) 12

13 DTD: Document Type Definition 1. Describes the structure of the document using grammar rules. 2. Describes in what sequence elements should appear in the documents. 3.A limited form of schema 4. Allows communities and companies to share XML documents following the same grammar rules. 5.AllowstheXMLdocumenttobeparsed automatically. 13

14 An Example of a DTD 1.A DTD for the XML document described earlier: <!DOCTYPE Stars[ <!ELEMENT STARS (STAR*)> <!ELEMENT STAR (NAME, ADDRESS+, MOVIES)> <!ELEMENT NAME (#PCDATA)> <!ELEMENT ADDRESS (STREET, CITY)> <!ELEMENT STREET (#PCDATA)> <!ELEMENT CITY (#PCDATA)> <!ELEMENT MOVIES (MOVIE*) <!ELEMENT MOVIE (TITLE, YEAR)> <!ELEMENT TITLE (#PCDATA)> <!ELEMENT YEAR (#PCDATA)> ]> 2. <!ELEMENT STAR (STAR*)> is a grammar rule, in BNF: STARS STAR (STARS, STAR are nonterminals.) 3.*: 0 or more times +: one or more times?: zero or one time : OR rules as in BNF 4.#PCDATA: Text data (parsed character data) 5. Example showing how to include DTD in XML document: 14

15 <?XML VERSION = "1.0" STANDALONE = "no"?> <!DOCTYPE Stars SYSTEM "star.dtd"> parameter STANDALONE= no says that a DTD is being used. 15

16 DTD with Attribute List 1. An element can have attributes with values that appear within the starttag. 2. Attribute values are strings. Example: <STAR starid="cf" starredin="sw, esb, rj"> 3. A tree representation with attribute list NAME STARS-MOVIES MOVIE: Return of the Jedi MOVIE: Empire Strikes Back STAR MOVIE STAR: Mark Hamill starredin starid cf ADDRESS ADDRESS starsof sw,esb,rj movieid TITLE YEAR sw cf, mh Carrie Fisher STREET CITY STREET CITY Star Wars 1977 Maple Hollywood Locust Malibu 16

17 DTD with Attribute List 1.<?XML VERSION = "1.0" STANDALONE = "n <!DOCTYPE Stars-Movies[ <!ELEMENT STARS-MOVIES (STAR*, MO <!ELEMENT STAR (NAME, ADDRESS+)> <!ATTLIST STAR starid ID starredin IDREFS> <!ELEMENT NAME (#PCDATA)> <!ELEMENT ADDRESS (STREET, CITY)> <!ELEMENT STREET (#PCDATA)> <!ELEMENT CITY (#PCDATA)> <!ELEMENT MOVIE (TITLE, YEAR)> <!ATTLIST MOVIE movieid ID starsof IDREFS> <!ELEMENT TITLE (#PCDATA)> <!ELEMENT YEAR (#PCDATA)> ]> 2.ID:avaluethatmustbeuniquewithin the document. 3.IDREF: refer to some ID 4. IDREFS: refer to several IDs. 17

18 (allows implementation of relationship types, 5. IDREFS avoids replication of MOVIES in the STARS. 6.There is no checking if incorrect id s are referenced. (starredin can have wrong ID s) 18

19 An XML-document satisfying the above DTD: 1. <STARS-MOVIES> <STAR starid = "cf" starredin = "sw,esb, rj"> <NAME> Carrie Fisher</NAME> <ADDRESS><STREET>123 Maple St.</STREET> <CITY>Hollywood</CITY></ADDRESS> <ADDRESS><STREET>5 Locust Ln.</STREET> <CITY>Malibu</CITY></ADDRESS> </STAR> <STAR starid = "mh" starredin = "sw,esb, rj"> <NAME> Mark Hamill</NAME> <ADDRESS><STREET>456 Oak Rd.</STREET> <CITY>Brentwood</CITY></ADDRESS> </STAR> <MOVIE movieid="sw" starsof = "cf", "mh"> <TITLE>Star Wars</TITLE> <YEAR>1977</YEAR> </MOVIE> <MOVIE movieid="esb" starsof = "cf", "mh"> <TITLE>Empire Strikes Back</TITLE> <YEAR>1980</YEAR> </MOVIE> <MOVIE movieid="rj" starsof = "cf", "mh"> <TITLE>Return of the Jedi</TITLE> <YEAR>1983</YEAR> </MOVIE> </STARS-MOVIES> 19

20 XML Schema 1. XML DTD is adequate for specifying tree structures with repeating elements 2. Data type in DTD is not very general and has its own special syntax. 3. XML need its own schema language 4. XMLschemaallowsuserdefinedtypestobecreated. 5. It uses the same syntax rules as regular XML documents, has its own schema definition language:w 6. Allows texts to be constrained to specific types. 7. Allows uniqueness and foreign key constraints. 8. Superset of DTDs <xsd: annotation> </xsd:annotation"> xsd-- xml schema definition 9. XMLSchema is significantly more complex. 20

21 Querying and Transformation 1. Relational: Query output of tables are tables 2.XML: Query output of XML documents are XML Documents 3. Transformation of Relational databases to XML documents for query and exchanges. Transform XML documents to relational. 4. Maintain XML documents as relational databases. (Need to transform XML documents to relational ) 21

22 XML Query Languages 1. Query language based on the Tree-model of XML data. 2. An element is a node and can have children nodes which can be subelements or attributes of the element. 3. Extension of simple path expressions of object-oriented and object-relational databases. 4. A sequence of node names separated by /. 5. Initial / represents the root (abstract) of the document. 6. Result of a path expression is a set of values. 22

23 Examples of XML Query Language: XPath 1. XPath is basic to most other XML query Languages. 2. It is based on tree paths. 3. Each element correspond to a node. 4. A node corresponding to an element (STAR) has child nodes that correspond to its subelements(name and ADDRESS). The node also has child nodes for the attributes (starid, starredin). 5. Values are at the leaves 6. A Graph for the previous XML-document: STAR starredin starid NAME ADDRESS ADDRESS STARS-MOVIES STAR: Mark Hamill cf sw,esb,rj MOVIE TITLE MOVIE: Return of the Jedi MOVIE: Empire Strikes Back YEAR starsof movieid sw cf, mh Carrie Fisher STREET CITY STREET CITY Star Wars 1977 Maple Hollywood Locust Malibu 7. XMLQuery: /STARS MOVIES/MOVIE/TITLE will return <TITLE>Star War</TITLE> <TITLE>Empire Strikes Back</TITLE> <TITLE>Return of the Jedi</TITLE> 23

24 8. XMLquery: /STARS MOVIES/MOVIE/TITLE/text() will return names without the tags. Star War Empire Strikes Back Return of the Jedi 9. XML Query: /ST ARS M OV IES/ST AR/@starId will return attribute values for starid: cf and mh 10. Selection Query: /STARS MOVIES/STAR[NAME = CarrieFisher ] will return STAR element for Carrie Fisher [NAME = CarrieFisher ]willallowtoselectall STAR nodes satisfying the qualification inside [ ] in the subtree rooted at STAR. <STAR starid = "cf" starredin = "sw,esb, rj"> <NAME> Carrie Fisher</NAME> <ADDRESS><STREET>123 Maple St.</STREET> <CITY>Hollywood</CITY></ADDRESS> <ADDRESS><STREET>5 Locust Ln.</STREET> <CITY>Malibu</CITY></ADDRESS> </STAR> 11. XMLQuery: /STARS MOVIES/STAR[NAME = CarrieF isher ]/@starid will return the value of the attribute starid of Carrie Fisher. cf 24

25 XML Query Language: XQuery 1. Includes XPath 2.Has similarity to SQL 3.One type of query is FLWR (pronounced like Flower) F (FOR): maps to elements, similar to SQL From L(Let): mapping complicated expression to variables W (Where): Similar to SQL Where R (Return: Select): construction of results Example: for $x in /Stars-Movies/STAR Where $x/name = "Carrie Fisher" Return <StarID> $x/@starid</starid> 25

26 Oracle XML 1. Based on Object Relational. 2. Available on SQL-PLUS 3. create table INVOICES of XMLTYPE; create table PURCHCASEORDERS ( PO_NUMBER NUMBER(4), PO_DETAILS XMLTYPE ) 26