|By Selim Mimaroglu||
|October 13, 2004 12:00 AM EDT||
This article looks in detail at how to generate XML data from your relational database. Although the examples were run on Oracle, very little of the code is Oracle specific. You can easily use all the ideas and examples presented here in other relational databases. We did this project at University of Massachusetts Boston as part of the Electronic Field Guide (EFG) project.
XML is the de facto standard for data exchange. It's simple, Unicode based, and platform independent. XML is a metadata language; it contains information about the data. All these features make it an attractive standard for exchanging data.
Why Generate XML from Relational Data?
Today most data (80% or more), is stored in relational databases such as Oracle, DB2, SQL Server 2000, and others. The Internet and Web services are present in our daily lives. A tremendous amount of data is transferred over the Internet between businesses. Data transfers may happen within a company, between different branches, or between different companies and individuals. No matter which of these situations applies to you, it's very likely that you will be asked to ship your data in XML, or that you are already doing it. Relational Database Management Systems (RDBMS) are still the best way to hold data in bulk. In the following paragraph we will give some information about our project and related resources that we used to provide relational data in XML.
Our XML project is part of the Electronic Field Guild (EFG). The EFG project is an object-oriented, Web-based database for the identification of species and recording of ecological observations. With funding from the National Science Foundation, this project is the result of the collaborative efforts between the Departments of Computer Science and Biology at the University of Massachusetts Boston. EFG queries the Integrated Taxonomic Information System (ITIS). On each query we only get a very small part of the ITIS database. XML can describe exactly what data it is delivering, and thus is the preferred format for the query results.
There are three ITIS branches: Canadian, Mexican, and U.S. U.S. ITIS provides the whole data in bulk (about 85MB), but, like many other organizations, it has been slow to join the modern trend to answer queries on it in XML format. Canadian ITIS provides query results in XML, but due to networking delays and some other problems, getting the result takes a long time. We decided to bring the whole database home and return the results of queries in XML format. We are using an RDBMS to store the bulk data. In the following paragraphs we will explain how to generate XML from this relational data.
This emerging standard enables us to generate XML fragments from relational data. Oracle and many other relational databases support the following standard SQL/XML functions. We will explain most of the SQL/XML functions, XMLElement, XMLAttributes, XMLForest, XMLAgg, and give an example for each.
As its name implies, this function generates an XML element. It takes an element name, an optional collection of attributes for the element, and zero or more arguments that make up the element content and returns an instance of type XMLType.
Table 1 is the schema of the "experts" table from our database. All the simple examples are related to this table, and Oracle was used for most cases.
Table 2 shows some of the data from the experts table.
WHERE expert_id BETWEEN 4 and 10;
XML2CLOB( XMLELEMENT(NAME "name", expert) )
WHERE expert_id BETWEEN 4 and 10
<name>Stotler, Raymond E.</name>
<name>Alfred L. Gardner</name>
<name>Steve J. Upton</name>
Here, name is the tag name; expert is the corresponding column name in the experts table. This query obtains the expert column value from the experts table and puts <name> and </name> tags around it.
This function simply creates attributes for an element. Listing 1 shows how it works.
Each name element has an id attribute. Each id attribute is obtained from the expert_id column value of the experts table. The XMLAttributes clause isn't used alone; it's used inside an XMLElement function. This makes sense since, in XML, an attribute is a name-value pair attached to the associated element's start tag.
The XMLForest() function produces a forest of XML elements from the given list of arguments. In other words, it produces many XML elements at a time.
In Listing 2, expert is the root element. The id, name, and info elements are children of expert element. The XMLForest function created three elements: the id element corresponds to expert_id column value; the name element corresponds to expert column value; and the info element corresponds to the exp_comment column value in experts table. Naming the elements in this function is accomplished by using AS keyword. For the first element it is expert_id as "id".
What if you don't specify an id (id = 6 in this example)? In this case you will have the appropriate XML fragment for each row.
XMLAgg() is an aggregate function that produces a forest of XML elements derived from a set of rows.
In Listing 3, there are five name elements as children of the experts root element. Without using XMLAgg() function it's impossible to have many name elements in a single XML document. If you don't use the XMLAgg() function and instead submit the query, you will get Listing 4.
That's not what we wanted. For this output, each experts element has only one name child element, and there are many experts elements. To combine information from multiple rows of the table we need to use the XMLAgg() function.
Creating hierarchical data is easy. Listing 5 shows you how to do this. You can use this idea in similar queries. This example involves the taxonomic_units table, which stores data about species, phyla, etc., i.e. nodes in the tree of life. Note the select within the select, to run through the inner loop.
I hope these examples have convinced you that it's possible to generate XML that obeys any XML Schema or DTD. You can use these functions, nested in each other, to display any kind of parent-child relation. Another such query could display all the experts for each taxon.
This is easy! You can start using these functions as soon as you finish reading this article. Being flexible adds value to this approach. An important point that's worth mentioning is that all the work is done inside the database by using the SQL/XML functions. In the Oracle case, all the work is done in the XML DB Engine. This is much faster and more efficient than doing the work outside the database. Another approach would be to get the data from the database and tag it outside the database for creating XML. This is possible but less efficient, more time consuming. The following are more advanced topics, such as XMLType View and XML Schema validation.
A view is a table that results from a subquery, but which has its own name and can be treated in most ways as if it were an ordinary table. Thus a view table is a logical window on selected data from the base tables and other views. XMLType views wrap the relational data in XML formats. In other words you can have a virtual XML file over your relational data inside the database. We can treat this new view as XML, and use XML specific operations on it, such as XPath and XQuery. These types of operations will be converted to corresponding SQL; this is known as query rewrite. You can create this view by using SQL/XML functions. Our SQL, which generates an XMLType view is shown in the source code, create.sql, online at www.syscon.com/xmlj/sourcec.cfm. Below is a simpler example, for better understanding.
SQL> CREATE OR REPLACE VIEW expert_view of XMLTYPE WITH OBJECT ID (EXTRACT(sys_nc_rowinfo$,'/experts/expert/@id').getnumberval()) AS SELECT XMLELEMENT("experts", XMLAGG( XMLELEMENT("expert", XMLATTRIBUTES(expert_id as "id"), expert))) FROM experts WHERE expert_id BETWEEN 4 and 10; View created.
This is how the view looks when you query it. This XMLType view is created over the experts table. The data displayed comes from the underlying relational table.
SQL> SELECT * FROM expert_view; SYS_NC_ROWINFO$ <experts> <expert id="4">Stotler, Raymond E.</expert> <expert id="5">Alfred L. Gardner</expert> <expert id="6">Steve J. Upton</expert> <expert id="8">Wayne Starnes</expert> <expert id="10">Lynne Parenti</expert> </experts>
It's possible to use XPath expressions on this view. Following is a query that has an XPath expression. This query extracts the value of an expert element that has an id attribute equal to 4.
SQL> SELECT extract(value(x), '/experts/expert[@id=4]') FROM expert_view x;
<expert id="4">Stotler, Raymond E.</expert>
First Step: Register an XSD
You can validate an XMLType instance against XML Schema Documentation (XSD) in Oracle. First, register the XSD in Oracle. Next, call a function that does the validation. There are several functions in Oracle for accomplishing this. Listing 6 is the only one shown, for simplicity.
This will register the XSD and name it as expert_view.xsd. You can name it anything you want of course.
Second Step: Validation
This section introduces isSchemaValid (argumet1, argument2). The first argument is the name of the registered XSD. The second argument is the name of the root element in the specified XSD. XSD can have more than one root. If the XML document (x in this case) is valid, this isSchemaValid returns 1.
SQL> select x.isSchemaValid('expert_view.xsd', 'experts') from expert_view x;
Putting It Together
For our project we generated XML that obeys our XML Schema Documentation (XSD)[itis.xsd]. Our SQL is shown in the source code for this article (available online at www.sys-con.com/xmlj/sourcec.cfm). It will output all the data in XML. As you can see, this query is significantly nested and long, but it's easy to understand (I hope). There are a few more functions in this query that we would like to mention: trim() simply gets rid of the white space in an entry and the to_char() function is used to change the date format. For example, to_char(v.up date_date, 'YYYY-MM-DD') will display the date as something like 2004-04-23. This is somewhat important because the date format in the database doesn't match the date format of the XML Schema.
In this project we deliver XML through a search server. Using this server, you can query the database by tsn, which is identical to the identification number of a taxonomic unit. e.g. a particular animal or plant. For this part of the project we used:
- Sun Enterprise 250 Server: 2 X UltraSPARC-II 400MHz, 2GB memory, SCSI disks
- Sun Solaris Operating System 5.8
- Oracle 9.2i
- JAVA 1.4.2
- Java Database Connectivity (JDBC) inside JavaBeans for connecting to and querying the database. We preferred the Oracle thin driver to the oci driver.
- JavaServer Pages (JSP) at the user interface level
- Tomcat 5.0.12
- Use Oracle Connection Pool
- Turn off the auto commit feature
- Use predefined column types in the select statement.
If you are not already doing so, you will probably be delivering your data in XML format soon. Keep in mind that most data resides in relational databases so generating XML from relational databases will be a very common task. Many of the database vendors, such as Oracle and DB2, provide the SQL/XML function support to make this task easier. SQL Server 2000 adds a new clause, the FOR XML clause, to the SELECT statement, which instructs SQL Server to return the result of a query in XML format.
Based on our experiments, generating XML data inside the database is fast; it took an average of 0.032 seconds per taxon query. Storing your data without the start and end tags is space efficient. Relational databases are very mature about storing, querying, and retrieving data quickly and efficiently. There has been over 20 years of work done in these technologies.
For larger projects, having XMLType views over the relational tables is advantageous. It gives you the chance to query the data using XPath and XQuery besides SQL.
In this article we provided some insight about SQL/XML functions, mentioned the benefits of storing data in relational databases, and explored the benefits of using XMLType views over relational data. For more detailed information about SQL/XML functions, check your database documentation.
The 4th International Internet of @ThingsExpo, co-located with the 17th International Cloud Expo - to be held November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA - announces that its Call for Papers is open. The Internet of Things (IoT) is the biggest idea since the creation of the Worldwide Web more than 20 years ago.
May. 30, 2015 12:00 PM EDT Reads: 1,793
The enterprise market will drive IoT device adoption over the next five years. In his session at @ThingsExpo, John Greenough, an analyst at BI Intelligence, division of Business Insider, will analyze how companies will adopt IoT products and the associated cost of adopting those products. John Greenough is the lead analyst covering the Internet of Things for BI Intelligence- Business Insider’s paid research service. Numerous IoT companies have cited his analysis of the IoT. Prior to joining BI Intelligence, he worked analyzing bank technology for Corporate Insight and The Clearing House Pay...
May. 30, 2015 11:45 AM EDT Reads: 578
As the Internet of Things unfolds, mobile and wearable devices are blurring the line between physical and digital, integrating ever more closely with our interests, our routines, our daily lives. Contextual computing and smart, sensor-equipped spaces bring the potential to walk through a world that recognizes us and responds accordingly. We become continuous transmitters and receivers of data. In his session at @ThingsExpo, Andrew Bolwell, Director of Innovation for HP's Printing and Personal Systems Group, discussed how key attributes of mobile technology – touch input, sensors, social, and ...
May. 30, 2015 11:30 AM EDT Reads: 4,027
All major researchers estimate there will be tens of billions devices - computers, smartphones, tablets, and sensors - connected to the Internet by 2020. This number will continue to grow at a rapid pace for the next several decades. With major technology companies and startups seriously embracing IoT strategies, now is the perfect time to attend @ThingsExpo, June 9-11, 2015, at the Javits Center in New York City. Learn what is going on, contribute to the discussions, and ensure that your enterprise is as "IoT-Ready" as it can be
May. 30, 2015 11:15 AM EDT Reads: 2,175
SYS-CON Events announced today that BMC will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. BMC delivers software solutions that help IT transform digital enterprises for the ultimate competitive business advantage. BMC has worked with thousands of leading companies to create and deliver powerful IT management services. From mainframe to cloud to mobile, BMC pairs high-speed digital innovation with robust IT industrialization – allowing customers to provide amazing user experiences with optimized IT per...
May. 30, 2015 11:15 AM EDT Reads: 1,089
The world is at a tipping point where the technology, the device and global adoption are converging to such a point that we will see an explosion of a world where smartphone devices not only allow us to talk to each other, but allow for communication between everything – serving as a central hub from which we control our world – MediaTek is at the heart of both driving this and allowing the markets to drive this reality forward themselves. The next wave of consumer gadgets is here – smart, connected, and small. If your ambitions are big, so are ours. In his session at @ThingsExpo, Jack Hu, D...
May. 30, 2015 11:15 AM EDT Reads: 839
The multi-trillion economic opportunity around the "Internet of Things" (IoT) is emerging as the hottest topic for investors in 2015. As we connect the physical world with information technology, data from actions, processes and the environment can increase sales, improve efficiencies, automate daily activities and minimize risk. In his session at @ThingsExpo, Ed Maguire, Senior Analyst at CLSA Americas, will describe what is new and different about IoT, explore financial, technological and real-world impact across consumer and business use cases. Why now? Significant corporate and venture...
May. 30, 2015 11:00 AM EDT Reads: 689
Today’s enterprise is being driven by disruptive competitive and human capital requirements to provide enterprise application access through not only desktops, but also mobile devices. To retrofit existing programs across all these devices using traditional programming methods is very costly and time consuming – often prohibitively so. In his session at @ThingsExpo, Jesse Shiah, CEO, President, and Co-Founder of AgilePoint Inc., discussed how you can create applications that run on all mobile devices as well as laptops and desktops using a visual drag-and-drop application – and eForms-buildi...
May. 30, 2015 11:00 AM EDT Reads: 5,504
SYS-CON Events announced today that MetraTech, now part of Ericsson, has been named “Silver Sponsor” of SYS-CON's 16th International Cloud Expo®, which will take place on June 9–11, 2015, at the Javits Center in New York, NY. Ericsson is the driving force behind the Networked Society- a world leader in communications infrastructure, software and services. Some 40% of the world’s mobile traffic runs through networks Ericsson has supplied, serving more than 2.5 billion subscribers.
May. 30, 2015 11:00 AM EDT Reads: 1,499
The Internet of Things is not only adding billions of sensors and billions of terabytes to the Internet. It is also forcing a fundamental change in the way we envision Information Technology. For the first time, more data is being created by devices at the edge of the Internet rather than from centralized systems. What does this mean for today's IT professional? In this Power Panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, panelists will addresses this very serious issue of profound change in the industry.
May. 30, 2015 11:00 AM EDT Reads: 1,044
"People are a lot more knowledgeable about APIs now. There are two types of people who work with APIs - IT people who want to use APIs for something internal and the product managers who want to do something outside APIs for people to connect to them," explained Roberto Medrano, Executive Vice President at SOA Software, in this SYS-CON.tv interview at Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
May. 30, 2015 10:30 AM EDT Reads: 4,371
WebRTC defines no default signaling protocol, causing fragmentation between WebRTC silos. SIP and XMPP provide possibilities, but come with considerable complexity and are not designed for use in a web environment. In his session at @ThingsExpo, Matthew Hodgson, technical co-founder of the Matrix.org, discussed how Matrix is a new non-profit Open Source Project that defines both a new HTTP-based standard for VoIP & IM signaling and provides reference implementations.
May. 30, 2015 10:30 AM EDT Reads: 5,242
SYS-CON Events announced today that O'Reilly Media has been named “Media Sponsor” of SYS-CON's 16th International Cloud Expo®, which will take place on June 9–11, 2015, at the Javits Center in New York City, NY. O'Reilly Media spreads the knowledge of innovators through its books, online services, magazines, and conferences. Since 1978, O'Reilly Media has been a chronicler and catalyst of cutting-edge development, homing in on the technology trends that really matter and spurring their adoption by amplifying "faint signals" from the alpha geeks who are creating the future. An active participa...
May. 30, 2015 10:30 AM EDT Reads: 890
There will be 150 billion connected devices by 2020. New digital businesses have already disrupted value chains across every industry. APIs are at the center of the digital business. You need to understand what assets you have that can be exposed digitally, what their digital value chain is, and how to create an effective business model around that value chain to compete in this economy. No enterprise can be complacent and not engage in the digital economy. Learn how to be the disruptor and not the disruptee.
May. 30, 2015 10:15 AM EDT Reads: 749
2015 predictions circa 1970: houses anticipate our needs and adapt, city infrastructure is citizen and situation aware, office buildings identify and preprocess you. Today smart buildings have no such collective conscience, no shared set of fundamental services to identify, predict and synchronize around us. LiveSpace and M2Mi are changing that. LiveSpace Smart Environment devices deliver over the M2Mi IoT Platform real time presence, awareness and intent analytics as a service to local connected devices. In her session at @ThingsExpo, Sarah Cooper, VP Business of Development at M2Mi, will d...
May. 30, 2015 10:00 AM EDT Reads: 682
Thanks to widespread Internet adoption and more than 10 billion connected devices around the world, companies became more excited than ever about the Internet of Things in 2014. Add in the hype around Google Glass and the Nest Thermostat, and nearly every business, including those from traditionally low-tech industries, wanted in. But despite the buzz, some very real business questions emerged – mainly, not if a device can be connected, or even when, but why? Why does connecting to the cloud create greater value for the user? Why do connected features improve the overall experience? And why do...
May. 30, 2015 09:45 AM EDT Reads: 746
Almost everyone sees the potential of Internet of Things but how can businesses truly unlock that potential. The key will be in the ability to discover business insight in the midst of an ocean of Big Data generated from billions of embedded devices via Systems of Discover. Businesses will also need to ensure that they can sustain that insight by leveraging the cloud for global reach, scale and elasticity.
May. 30, 2015 09:30 AM EDT Reads: 6,656
Imagine a world where targeting, attribution, and analytics are just as intrinsic to the physical world as they currently are to display advertising. Advances in technologies and changes in consumer behavior have opened the door to a whole new category of personalized marketing experience based on direct interactions with products. The products themselves now have a voice. What will they say? Who will control it? And what does it take for brands to win in this new world? In his session at @ThingsExpo, Zack Bennett, Vice President of Customer Success at EVRYTHNG, will answer these questions a...
May. 30, 2015 09:15 AM EDT Reads: 629
With major technology companies and startups seriously embracing IoT strategies, now is the perfect time to attend @ThingsExpo in Silicon Valley. Learn what is going on, contribute to the discussions, and ensure that your enterprise is as "IoT-Ready" as it can be! Internet of @ThingsExpo, taking place Nov 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 17th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The Internet of Things (IoT) is the most profound change in personal an...
May. 30, 2015 09:00 AM EDT Reads: 2,528
We’re entering a new era of computing technology that many are calling the Internet of Things (IoT). Machine to machine, machine to infrastructure, machine to environment, the Internet of Everything, the Internet of Intelligent Things, intelligent systems – call it what you want, but it’s happening, and its potential is huge. IoT is comprised of smart machines interacting and communicating with other machines, objects, environments and infrastructures. As a result, huge volumes of data are being generated, and that data is being processed into useful actions that can “command and control” thi...
May. 30, 2015 08:00 AM EDT Reads: 920