Working with XML and DB2

Transcription

1 Working with XML and DB2

2 What is XML? XML stands for EXtensible Markup Language XML is a markup language much like HTML XML was designed to carry data, not to display data XML tags are not predefined. You must define your own tags XML is designed to be self-descriptive XML is a W3C Recommendation XML does not DO anything. XML was created to structure, store, and transport information.

3 What is XML?

4 XML and Database Relationship Storing XML in Files Low performance regarding search within the files Store XML within a single field in a relational Database Need of searching and retrieving data that appears within the XML data

5 DB2 purexml DB2 stores information as actual XML elements and XML attributes, allowing faster data insertion into the database and faster retrieval of information.

6 Working with XML and DB2 Download DB2 from Perform the installation following the instruction provided by the setup wizard.

7 Creating a Database To setup a database table for purexml is to indicate that an area of the database will contain XML data. Open the command window Enter the following command: CREATE DATABASE test USING CODESET utf-8 TERRITORY BR After created the database connect to it performing the folowing: CONNECT TO test

8 Creating Tables To create a table within the a database, once connect to it enter the command below: CREATE TABLE food ( id INT PRIMARY KEY NOT NULL, content XML)

9 Inserting XML Data into the Database To insert data into a table the INSERT command can be used as the example below INSERT INTO food values (1, <food><name>spaghetti</name><price>10.90</price><calories>30 00</calories></food> ) INSERT INTO food values (2, <food><name>lasagna</name><price>12.30</price><calories>80 000</calories></food> )

10 View Data To view data using normal SQL simply use the usual select statement shown below SELECT * FROM food If the command is executed from the command window the XML data is shown like a text field. To get a better view run the query from the command editor

11 Viewing Data from the Command Editor Right click on the DB2 green container icon in the windows system tray.

12 Viewing Data from the Command Editor When the select statement is performed the screen below is shown

13 Viewing Data from the Command Editor To see the XML, click on in the Content column

14 Updating XML Data To update XML data use the command below UPDATE food SET content = XMLPARSE (DOCUMENT ('<food><name>lasagna</name><price>20.30</price><calories>80 000</calories></food>')) where id=1 The XMLPARSE function parses the argument as an XML document and returns an XML value. DOCUMENT Specifies that the character string expression to be parsed must evaluate to a well-formed XML document that conforms to XML 1.0, as modified by the XML Namespaces recommendation

15 SQL, SQL/XML and XQuery SQL allow users to update or retrieve information in a relational database. If you want to issue queries against the individual pieces of information in the XML data, you can use XML extensions to SQL or a new query language called XQuery. DB2 provides two ways to issue queries for information in XML data - XQuery - SQL/XML

16 XQuery

17 XQuery Has many features of a programming language like variables, data types, operators, conditional expressions, functions and so on. Two of the most important types of expressions in XQuery are - FLWOR expressions - XPath expressions

18 XQuery - FLWOR Is similar to SELECT-FROM-WHERE expression Below are a list of clauses used to handle with FLWOR XQueries for specifies the iteration sequence. In other words, this clause specifies how many times XQuery executes the sequence of clauses. A variable indicates the current iteration. let - declares a variable and assigns a value to the variable. You can assign any value to this variable, including a list containing multiple items. where - specifies criteria for filtering the information that is returned. order by - specifies the order of the information that is returned. return specifies the information that is returned.

19 Running a XQuery To retrieve a certain data from the XML column within the table enter the following command: xquery for $y in db2-fn:xmlcolumn( FOOD.CONTENT )/food where $y/calories > return $y/name The statement above will bring all the food s name where its calories are bigger then 20000

20 XPath

21 XPath XPath allows you to identify information in XML data. XPath expressions let you specify the path to the XML data you want. They also allow conditions that must be met in order the information to be returned. Follow an example below: $y/food/calories > 20000

22 SQL/XML SQL/XML is a set of extensions to SQL for working with XML data such as - The XML data type. - The ability to use XPath and XQuery to search for specific information in XML data. - Functions that allow you to publish relational data in XML format. - Functions that allow you to convert relational data to XML data, and vice versa. - Functions to validate XML data against XML schemas Enter the SQL/XML query below to see the data within the XML select content from food where xmlexists('$d/food[calories="80000"]' passing food.content as "d")

23 Comparing XQuery and SQL/XML

24 How to Identify Information with XPath Visualize XML as a hierarchical tree of nodes. You can use XPath to retrieve information from one or more of those nodes. To choose XML nodes, XPath uses expressions that include - The path to nodes - Filters - Operators

25 The Path to Nodes

26 Node Selection Expressions

27 Filters

28 Hands On 1 Create two XML files one for Products (Tags: Code, Name, Brand, Price, Color) and one for Client (Tags: Code, Name, Age, Address, ProdCode) 2 - Create an XML based database called 'class. 3 - Create a table called 'Product' (info xml) and one called 'Client' (info xml). 4 - Poupulate those tables. 5 - Select all data from the Product Table.

29 Hands On 6 Select all data from the Client Table. 7 - Select the product name where price is greater then $ Select Client name where age greater then 50 and Product Code equals 1. 9 Select all products name and price that has a client who bought it and its client name order by client name. 10 Select all products that was not bought yet.

30 Working with Indexes

31 Improving Performance Using Index When a speed up on the retrieval of information on a database is needed an index could be created. Index is like a table with two columns: One column contains the information that you use when searching and the other column contains a pointer to the information in the database.

32 Improving Performance Using Index Using an index is faster than searching the database table for two reasons. - Because index rows are smaller in size than corresponding database table rows, you can fit more of them in a physical file block. - Indexes order items sequentially based upon the information you are searching against. This sequential approach allows for the use of some very fast search techniques.

33 Relational versus XML Indexes An XML index is different than a relational index in the following ways: - You can specify only one column in an XML index - You can have zero, one or multiple XML nodes in each cell of the database column matching the specified XML pattern. Therefore you can have multiple index entries for a single row in a table - You can have multiple indexes for a single XML column, with each index related to a different portion of the XML

34 Creating an Index To create an index for purexml data, use the CREATE INDEX statement. In addition to specifying the column to index, you also specify an XML pattern that identifies the information within the XML data, and specify the data type of that information. CREATE INDEX findex on Food(content) GENERATE KEY USING XMLPATTERN /food/name as SQL DATE

35 Importing XML Data

36 Importing XML Data The IMPORT facility loads data from a delimited ASCII file. Each line of the ASCII file represents a row of the database. In each line, a delimiter separates the data for each column. It s necessary to create a file under the XDS (XML Data Specifier) to point to the actual XML file. The IMPORT command should be used as follows: IMPORT FROM ASCII_file.del OF DEL XML FROM actual_xml_file INSERT INTO schema.table

37 Importing XML Data In the method shown in the last slide, each XML file contains the XML data for a single database cell. To include a reference to an external file that contains the XML data, you use the XML Data Specifier (XDS) Syntax. XDS Syntax Example: <XDS FIL='myexport.txt.001.xml' OFF='0' LEN='119' />

38 Get Up to Date with DB2 purexml!

39 Resources and News There are many free online resources to take advantage on the web. Following a list with some tutorials and news. Free Books Tutorials Forums art=0

40 Resources and News PureXML Network and Blog

41 Bibliography DB2 purexml for Dummies, Conor O Mahony, Wiley Publishing purexml SQL/XML & XQuery, Raul F. Chong, IBM Toronto Lab