Book Review: Processing XML documents with Oracle JDeveloper 11g

Written by Paweł Barut
This time I would like to recommend a book Processing XML documents with Oracle JDeveloper 11g published by PacktPub.com. As I have some experience with XML processing inside Oracle DB (XMLDB) I was lacking the knowledge of XML manipulation in Java, especially using Oracle JDeveloper. This book is rather not for beginners - you should have basic knowledge of what is XML, at least theoretically. From the book you can learn how to manage XML Schemas in JDeveloper, then write XML documents based on those schema and finally validate them in JDeveloper or write Java code to validate it automatically. Chapters that I value much are those describing how to generate PDF documents. There are two methods described - one using Apache FOP API , and Oracle XML Publisher. As I was not generating PDF's this way so far, I found those 2 chapters very interesting. There is also chapter on generatin Excel by transformation of XML using Apache HSSF API .

Book is very practical. If you want to start with subjects described above then this book is for you. Of course it does not mean that you do not have to study documentation. However, it will be easier for you to make first steps. Beside describing Oracle JDeveloper, author also shows how to install and use Oracle Berkley XML DB to store, query and update XML Documents - using command line and XML DB API.

I especially recommend eBook version. All URLs in eBook version are active, so linking to web pages are very simple. Also coping sample code is easy. This book contains many practical and usefull tips on XML processing and tools as well. So if those XML aspects are in your interest, then it's definitelly good to invest in this book.

Keep reading,
Paweł

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Multiplying texts and null effect

Written by Paweł Barut
This time short notice on side effect of implicit type conversion ans short expression evaluation. Let me show this on example - try this statement:

SQL> select 'a'*'b' from dual;
select 'a'*'b' from dual
       *
ERROR at line 1:
ORA-01722: invalid number

As expected we get error. It is due to fact that multiplexing operator (*) is expecting numbers on both sides, an implicit conversion takes place. However this statement:

SQL> select ''*'b' from dual;

    ''*'B'
----------

does not give error. How is it possible? In oracle empty string is in fact an null. null multiplied by any number gives null, so due to optimization oracle decided to evaluate this expression to null.
As you know also 0 (zero) multiplied by any number gives zero. So let's test it:

SQL> select '0'*'b' from dual;
select '0'*'b' from dual
           *
ERROR at line 1:
ORA-01722: invalid number

In that case Oracle did not optimized evaluation, and decided to make full calculation. I do not know the reason for different behaviour but is repeatable (at least on instances I've access to).
My recommendation: always make sure that you provide data in proper data-type. Make explicit data conversion using to_number, to_date or to_char functions.

Keep reading,
Paweł

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