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_____________________________________________________________________________ Copyright© 2012 by HowardHyde. All rights reserved

JAVA WEB

DATABASE APPLICATION DEVELOPMENT

VOLUME I:

FROM SQL AND JDBC TO HTML AND BACK

SNEAK PEEK FIRST EDITION 1.0.1 - JANUARY 2012

Howard Hyde

www.JavaWebDB.com

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Java Web Database Application Development Copyright© 2012 by Howard Hyde. All rights reserved.

CONTENTS

CONTENTS 2

PREFACE 4 Value Proposition 4 Biases 4 How to read this book: 5

PART I: FROM SQL AND JDBC TO HTML AND BACK 7

CHAPTER 1: SERVLETS, JSP, JDBC 8 The Rationale and Purpose of Java Servlets 8 Application Components and Infrastructure 8 One-Minute Java Primer 12 Coding Servlets and Java Server Pages (JSP) 14

CHAPTER 2: YOUR FIRST JAVA WEB APP 18 Installing the source code 18 A trivial JSP application: (Bogus) Stock Quoter 18 The same app written as a servlet 24 A variation on the servlet-based implementation 34 The same app enhanced with Javascript and Cascading Style Sheets (CSS) 42 Summary 51

CHAPTER 3: INTRO TO JDBC 52 JDBC 52 JDBC Drivers 52 Database Connnectivity Architecture 53 JDBC Connection Parameters 55 JDBC Objects and Methods to establish the connection 56 JDBC Objects and Methods to execute an SQL Query 59 JDBC Objects and Methods to execute SQL DML 60 JDBC Objects and Methods to execute Stored Procedures 61 JDBC Exceptions 62 Summary 62

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CHAPTER 4: YOUR FIRST JAVA WEB DATABASE APP 63 Example Application: Aviation Scheduling: ‘FBO Ace’ 63 Database Setup and Design 65 Application Architecture: Model/Data, View, Controller 67 Airport.java 67 Digression regarding data bean code generation 70 Digression regarding error handling and communication 71 Query and Persistence Methods 73 Application Home Page: Index.jsp 80 The Database Application Configuration (web.xml) File 82 Outlining Your First Database Servlet: AirportServlet.java 84 Coding the Servlet 85 processPageBody() 88 airportViewEditForm() 91 persist() 94 getJDBC2Connection() 97

CHAPTER 5: DATABASE CONNECTION POOLING AND JNDI 98 Configuration Checklist 98 Coding the app to use JNDI JDBC resources 100

CHAPTER 6: NUMBERS, DATES, LISTS AND BOOLEANS 103 The Aircraft Table 103 Data Bean Template 104 Aircraft.java 110 The Aircraft Data Maintenance Form 115 Configuring The Aircraft Servlet 117 The Aircraft Servlet Code 119 The UI method: aircraftViewEditForm() 122 The Save method: persist() 133

CHAPTER 7: DATA MODULES WITH FOREIGN KEY LOOKUPS 140 Example Application: Aviation 140 Database App 3: Flight with FK References to Aircaft and Airport. 146 Airport.java, Aircraft.java and Flight.java 148 Digression: Active/Emphatic vs. Passive NULL 152 Setters and updateStatus(): Intelligent update control 155 Retrieval methods 158 Heavy lifting: saveToDatabase() 159

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Delete and Commit 166 FlightServlet.java 169

CHAPTER 8: COMPLEX MASTER-DETAIL DATA MODULES 188 DBWebApp04 Home Page: Index.jsp 188 Airport, Aircraft, Pilot and Flight_Pilot_Type Modules 190 The Master-Detail Flight Module 194 import com.RADInfoDesign.jwdbappdev.util.Util; 200 Abstract class DBAppDataBean 202 Flight.java 209 Flight_Pilot.java 218 FlightServlet.java 220 processPageBody() 223 flightViewEditForm() 229 JDBC Transaction Autocommit Mode 241 persist() 241

CHAPTER 9: EPILOGUE TO PART I 251

PART II: PERSISTENCE APIS AND FRAMEWORKS 258 COMING SOON IN VOLUME II 258

PART III: ENTERPRISE APPLICATION ARCHITECTURE CONSIDERATIONS 259 COMING SOON IN VOLUME III 259

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PREFACE

Value Proposition

Other fine books are available on Java-based database and web technologies such as SQL,

JDBC, JNDI, Servlets, JSP, Javascript, CSS etc. What this book intends to offer is a unique

synthesis of the above, from a unique perspective deeply rooted in the relational paradigm,

which challenges you the Java programmer to make a true value-added contribution to the

architecture.

I will confess my utter lack of visual or graphic design skills, while assuring the artists in

my audience that their work will given their place in the architecture to plug in and work

their magic.

Biases

There are unlimited variations possible in approaches to software development with a

single technology, to say nothing of a system that in pursuit of a comprehensive solution

combines a dozen significant technologies, some of which may be supported by different

vendor’s products. In particular, the examples in this book were developed and are

demonstrated on a specific platform:

Database: Oracle. We don’t get into advanced features of the relational database

management system (RDBMS), but there will be minor syntactical variations

between the examples in this book and your database, if it is MySQL, MS SQL

Server, IBM DB2, Sybase, Informix, or another.

Web/Application Server: Apache Tomcat. Again, we will not go very deep

into proprietary features, so with the exception of variations related to JNDI and

database connection pooling (subject of Chapter 5), your application should run

without modification on any JEE-compliant server platform: Weblogic, JBoss,

GlassFish, Websphere etc.

Java Servlets. Servlets are the dominant technology we will use to impement the

Controller and View (dynamic HTML embedded in Java) functions of our

application, with standard (and not-so-standard) Javabean classes performing the

Model/data function. Other approaches are possible including those that emphasize

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Java Server Pages (JSP), Java Server Faces (JSF) and/or Enterprise Java Beans

(EJB). Even so, servlets are the common denominator and underlying engine of all

of these options. They offer a rich and highly practical platform (at the very least a

very effective training ground) for development of web-based applications, giving

the developer complete programatic control. Even if you consider JSF to be the new

supersonic fighter jet with all-electronic instruments (‘glass cockpit’) and fly-by-

wire controls, it will pay dividends to learn first to fly a propeller airplane with

gyroscopic, magnetic and pitot-static instruments1 and mechanical, pulley-and-

cable controls (servlets are a cut above that!).

Some of my biases go beyond the choice of vendor’s products and technologies and extend

to methodologies and design paradigms. Some readers will disagree with my approach. To

those I hope that even in disagreement you can use my examples as a point of departure for

alternatives. And I welcome your comments and feedback. This is a journey that never

ends.

How to read this book:

Hint: Start on Chapter 1 (or 2 if 1 is too elementary for you) and turn the pages one

by one until you get to the end.

That’s not too difficult to get, is it? All of the sample applications and tutorials build upon

one another, starting with the most simple, minimalist elements necessary to get an app

functioning round-trip from the database to the user’s browser and back; then

incrementally increasing the complexity and advancing to more enterprise-scalable

solutions. Advanced pros may skim to accelerate to the parts more interesting to them, but

if you skip sections or chapters entirely, some lessons and tutorials might not make sense;

you won’t understand the rationale behind the methodology.

So strap in for a step-by-step, progressive journey as opposed to a random access to a reference

book.

1 Aviation metaphors will pervade this volume.

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PART I: FROM SQL AND JDBC TO HTML AND BACK

In this part, we’ll get you productive as quickly as possible with the basic concepts and

mechanics of database application development with JSP and Java servlets. We outline

the architecture, introduce our example application data model, expose the essential JDBC

and servlet classes and methods, and get our hands dirty with a working, full data lifecycle

web application.

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CHAPTER 1: SERVLETS, JSP, JDBC AND DATABASE

The Rationale and Purpose of Java Servlets

Java servlet technology allows client applications running in a browser over a TCP/IP

network (like the Internet, internal enterprise ‘intranets’ or external ‘extranets’) to invoke

complex programmatic functionality that goes beyond simple retrieval of static HTML and

graphic files. It offers significant performance and other improvements over the earlier

Common Gateway Interface (CGI) technology that was first developed in the early 1990’s

to provide this capability. CGI programs had to wake up, allocate memory, execute,

deallocate memory and die with each client request, thereby creating a heavy, poorly-

scaling overhead burden without any possibility of managing session state. Servlets on the

other hand stay resident in memory to serve a theoretically unlimited number of requests.

Servlets can maintain global attributes across requests such as persistent database

connections. And they’re written in the platform-independent, powerful and popular

object-oriented language of Java.

Application Components and Infrastructure

When we discuss servlet development, there are certain assumptions that may be made

about the system architecture, or ‘platform’ for which we are developing.

Servlets do not have a graphical user interface (GUI) of their own; they execute within the

memory space of a webserver ‘container’ residing on a server machine, typically in a back-

office data center. Servlets may write output to the server console, but their primary

function is to process HTTP requests received from browser clients and to send responses

back in the form of HTML and related content which the browser may render graphically

for the user.

So we assume the presence of the following application components:

TCP/IP network: Transport Control Protocol / Internet Protocol is the fundamental

communication mechanism of the Internet, and all vendors of Local Area Network …

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CHAPTER 2: YOUR FIRST JAVA WEB APP

This chapter will demonstrate the basic mechanics of the HTTP request/response cycle as

implemented with JSP and Servlets. We will leave the database aside for the moment.

Installing the source code

The source code for the 8 sample applications that we will walk through in the next

chapters is in the file bundle that accompanies this book, under the directory /webapps, in

the following subdirectories:

/webapps

o /BogusStockQuote01




o /DBWebApp01

o /DBWebApp02

o /DBWebApp03

o /DBWebApp04

You should be able to drop these directories and their files into the deployment directory of

your web/application server (/webapps in the case of Tomcat) and run the apps. Starting

with /DBWebApp01, the database apps will require customization of the web.xml

configuration file to match the database connection parameters specific to your

environment.

A trivial JSP application: (Bogus) Stock Quoter

Our first app will consist of just two JSP files. When a user invokes a valid application URL from a browser without specifying the exact file (or servlet) name, the server will either display a directory listing or invoke a ‘welcome file’. Which file serves (or may serve, in

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CHAPTER 3: INTRO TO JDBC

In this chapter, we present bare-bones essential information on how Java applications

communicate with relational databases. This will pave the way for our first sample Java

web database application in the next chapter.

JDBCJDBC™is a trademarked technology created by Sun Microsystems for communicating

between Java clients and relational databases. JDBC provides classes and methods for a

Java-based clients to:

connect to a database define and execute queries (SQL SELECT) against a database define and execute SQL DML (insert, update, delete) against a database define and execute stored procedures with IN, OUT, and INOUT parameters retrieve results sets, OUT parameter values and return values from database queries

and stored procedures. …and much more.

The next several sections will detail the basics of using JDBC with servlets.

JDBC DriversThe main manifestation of the JDBC technology is the driver, the piece of software that

translates Java code and objects into commands and datatypes compatible with the SQL

database you are connecting to, and manages the communication. JDBC drivers are

classified by Type, of which there are 4:

1. JDBC-ODBC bridge. In this model, the JDBC driver acts as a Java wrapper around the

more generic industry-standard ODBC driver. An additional ODBC driver is required.

2. Native API – Partly Java Driver. This type of driver communicates to each database in its

proprietary protocol, but the driver itself is only partly implemented in Java and therefore

requires additional platform-specific binary code, such as Windows DLL’s.

3. JDBC-Net Pure Java Driver. This driver is implemented entirely in Java and

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CHAPTER 4: YOUR FIRST JAVA WEB DATABASE APP

In this chapter we’ll develop an application which queries, displays and provides insert,

update and delete functionality on rows of a single database table with simple datatypes.

In the process we’ll learn a bit more about using JDBC database connections, and how to

divide data, presentation and application functionality responsibility among Javabeans (or

‘Java data beans’), view and controler (servlet) classes and methods. These elements will

evolve in the rest of the book as we explore database applications of increasing complexity.

(See source code subdirectory /DBWebApp01 for this chapter’s application.)

Example Application: Aviation Scheduling: ‘FBO Ace’The application and code examples in this book are mostly based on a very basic version of

an aviation scheduling database system I call ‘FBO Ace’ (FBO stands for Fixed Base

Operator, which is a term used to describe businesses that offer fuel, maintenance,

scheduling and pilot training services in the General Aviation industry). In later chapters

we will present the complete database schema; for this chapter we will introduce just one

table in the schema: ‘Airport’.

Two main views of this table will be presented to the user in the browser UI:

A read-only listing, and

An editable data maintenance form with options to create new and modify or purge

existing instances.

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CHAPTER 5: DATABASE CONNECTION POOLING AND JNDI

The way we used database connections in our introductory database application served its

purpose, but now we need to get a bit more serious about a database connectivity

architecture and methodology that will scale and perform. For this we need the Java

Naming and Directory Interface, or JNDI.

With JNDI, database connections and other external resources are managed by your

container, the web or application server (Tomcat, JBoss, Glassfish, Weblogic, Websphere

etc.), separate from your servlets, javabeans, enterprise javabeans (EJBs) or other

application classes; and made available to your application classes to use, minimizing the

connection management code that you have to write.

JNDI has a scope beyond just database connections and JDBC; it can be used to facilitate

remote communication among generic Javabeans, UserDatabases (named accounts of

web/application server uses), JavaMail sessions and more. For our purposes, we are only

interested in the database connection pooling and JDBC-related features.

Because configuring JNDI varies so widely from vendor to vendor, we will concentrate here

on basic principles and a few particulars specific to Tomcat, and let you browse the vendor-

specific documentation for greater depth.

Working with technical documentation from vendors and reference sites can be an exercise

in frustration. I remember well when I was first learning this a decade ago, trying several

configurations that I thought should have been correct, only to get error messages when I

attempted to run my app. When I finally found a configuration that worked, I realized that

some elements I had put in place (because the documentation told me to) were

superfluous, and so I removed them.

Configuration Checklist

The example JDBC/JNDI configuration values we show in this chapter is what we will use

for our second database application which will be elaborated in the next chapter.

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CHAPTER 6: NUMBERS, DATES, LISTS AND BOOLEANS

In Chapter 4 we created a data maintenance form on a simple, single table with only

textual datatypes (the Airport_ID is numeric, but since it’s not ‘mathematical’ we could

treat it in Java as a String). In this chapter we’ll go another round with a single table data

module, but introduce more datatype issues.

In this chapter we’ll deal with slightly more complex issues: dealing from the database to

the UI and back with numbers, dates, lists and ranges of permissible values, and (quasi-)

boolean datatypes rendered as checkboxes. Along the way we’ll refine the craft of using

metadata queries to generate clean, consistent code against table and column structures

and datatypes.


The Aircraft Table

Last time we introduced the Airport table of our aviation scheduling schema. For this

chapter we introduce the Aircraft table:

Here is the SQL DDL to create this table, which reveals the more subtle details of its

definition, including datatypes and check constraints: CREATE TABLE AIRCRAFT ( AIRCRAFT_ID NUMBER NOT NULL, NAME VARCHAR2 (20) NOT NULL, WING_TYPE VARCHAR2 (11) NOT NULL, DESCRIPTION VARCHAR2 (4000), MANUFACTURE_YEAR NUMBER (4) NOT NULL, NEXT_MAINTENANCE_DATE DATE NOT NULL, IN_SERVICE_FLAG CHAR(1) NOT NULL); ALTER TABLE AIRCRAFT ADD CONSTRAINT AIRCRAFT_PK PRIMARY KEY (AIRCRAFT_ID);

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CHAPTER 7: DATA MODULES WITH FOREIGN KEY LOOKUPS

As our database application gets increasingly elaborated, it is time to lay out the complete

database schema design for the following few chapters. We will only an app against 3 of the

6 tables in the complete schema in this chapter. In the next chapter, we will use all 6.


Example Application: Aviation

The example application subject is aviation: scheduling flights matching pilots to aircraft

travelling between airports. The model and table attributes will be kept very simple

(please, no complaints that you can’t run Virgin InterGalacticWarp Airlines on these six

tables).

As we stated earlier, we use a surrogate-key design, where tables have one or more

meaningless numeric columns comprising its primary key; in addition, some tables will

have alternate unique keys for natural business-level identifiers.

The Data Model

Here are the tables we will create for this model (the first two we have seen already):

Airport: This table contains your complete list of all airports served by your

organization (or used, unofficially, as emergency landing strips); each row

represents a potential departure or destination point for a Flight. Alternate keys

Name and on the 3-character code (such as ‘LAX’, ‘JFK’, ‘CDG’ etc).

Aircraft: Each row represents a specific air travel vehicle; taken in the aggregate,

this entity represents the organization’s fleet. Alternate key on ‘name’ column,

which in practice here represents the registration or ‘N-’ number (in the United

States), i.e. ‘N742ST’.

Flight: Represents a scheduled instance of one or more Pilots flying an aircraft

between airports. Alternate unique key on business-level ‘Flight_Number’ column,

which can be an alphanumeric value entered manually or derived from other

attributes or automated algorithm as required.

Pilot: Person qualified to manage the controls of an aircraft in flight.

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CHAPTER 8: COMPLEX MASTER-DETAIL DATA MODULES

In Chapter 7 we completed our 6-table data model and schema, and built an app that

operated on one and referenced two more. Here we will complete an app that provides the

user with data maintenance forms against all 6 tables, including a capstone module that

allows editing of new or existing Flights and Flight-Pilots in a master-detail form with

references to the other 4 tables; all 6 tables represented in a single cohesive business

object.


DBWebApp04 Home Page: Index.jsp

Below is the new Home or landing page for the app. As you see, it is a menu offering

navigation to all of the individual data modules.

Figure 8-1: DBWebApp04 / FBO Ace Home Page

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The Master-Detail Flight Module

The real ‘red meat’ of this chapter is the new Flight module, which allows the user to add or

edit multiple records from 2 tables simultaneously in a Master-Detail view. The landing

page for the Flight servlet is (as usual) the read-only/List view. The reader will notice 3

new elements this time:

A link back to the Main Menu (index.jsp a.k.a. Home page)

A button labeled ‘Create New’

‘Edit’ buttons in each row of the list view table.

Here’s what it looks like:

Figure 8-2: Master-Detail Flight Module in Read-Only/LIST mode

Instead of having the user edit all flights at once, clicking on the [Edit…] button in a chosen

row brings up the Edit form for that flight, with the master Flight record displayed in a top

block and the detail Flight-Pilot records shown in a separate block below.

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Here’s how it looks:

Figure 8-3: Master-Detail Flight Module in EDIT Mode

The reader will note that the Master block is shown this time with Flight attibutes listed

vertically, while the child block retains the columnar grid design established earlier.

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The four referenced tables are represented as pull-down menus from which the user may

make choices:

Figure 8-4: Drop-Down FK List Boxes on Edit Flight Form

Other elements to note:

The user may modify any of the elements of Flight or Flight-Pilot by editing the

fields or making pull-down menu choices in place, then clicking [Save to Database.]

New Flight-Pilot records may be added one at a time in the child block. Adding new

whole Flights requires entering the form from the List view in New mode by clicking

that form’s [Create New…] button (see below).

Existing Flight-Pilot records may be deleted in the usual way; check the box in the

[Delete?] column of the child grid in the intended row and then click [Save to

Database].

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The Pilot field in the child Flight-Pilot block is read-only for exising records,

selectable for new records. Pilot_ID is a member (co-equal with Flight_ID) of the

primary key of the Flight_Pilot table; part of its fundamental definition which

ensures that a given Pilot may only be assigned to a given flight once. If one Pilot

should be exchanged for another for a given Flight, this requires a delete-insert;

delete the old, insert the replacement.

The user may (attempt to) delete the Flight by checking the [Delete?] checkbox at

the bottom of the master block and clicking [Save to Database]. What happens next

depends on whether there are any child records in the Flight-Pilot block and

whether or not the foreign key from flight_pilot to flight is enforced, and whether or

not CASCADE DELETE is implemented on the foreign key. In case of a constraint

violation, the SQL statement will fail and the user will receive a message such as:

“Sorry, SQL Delete failed. This may be a business rule violation or a program bug. If

you think it is a bug, Please contact support at 1(800)FAT-CHANCE.”

If on the other hand the SQL delete succeeds, the user is returned to the List view of

the Flight module.

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Clicking the [Create New…] button on the List screen brings up a form similar to the one

we just saw, except with all fields blank and no pull-down menu choices pre-selected.

Figure 8-5: Master-Detail Flight Module in NEW Mode

This screen permits the user to create up to 1 new Flight plus 1 new related Flight-Pilot

record at a time (Flight-Pilot records may NOT be created indepenently of Flights in our

app). Upon Save, the user is returned to the Edit form for the same Flight, where (s)he

may edit the records just created and/or add more Flight-Pilot records.

That’s how it looks and feels (with rudimentary visual design). Now let’s dive into the guts

of how it is built.

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CHAPTER 9: EPILOGUE TO PART I

We’ve come a long way. We started with the simplest of all possible database applications,

a single table with a few text columns in it, and figured out the minimum 3-tier

infrastructure needed to make that available to multiple users over the web. From there we

proceeded by increments to deal with more complex data types and relationships and to

reinforce the architecture (such as connection pooling) to make the solution scalable for

large enterprises, datastores and user populations. Along the way, we practiced functional

decomposition and the separation of model, view and controller functions; created a

standard servlet-and-Javabean class and method framework for the complete cycle of

database interactivity; established a flexible methodology for formatting, presenting and

receiving dates and date-time values; built minimalist logic to interpret the user’s intent

with respect to the creation, modification and/or erasure of data; put in safeguards against

crippling NullPointerExceptions; and more.

Our capstone application blended the object-oriented and relational paradigms to escape

the prison of the one-class-one-table model and establish a new standard unit of

interaction:

The rich business object having one unitary driving entity (Flight), one or more

potentially multi-valued child entities (Flight-Pilot) and any number of referenced

entities, qualifiers or dimensions (Airport, Aircraft, Flight Pilot Type, Pilot), any of

which could be the driving entity of its own simple or complex business object.

From that unit, enterprise applications of any extent may be constructed.

Even so, there is so much more we could do, right? Here are some advanced topics that

could be developed in a future expanded edition of this book (for now, they are YOUR

extra-credit assignments):

Working with advanced datatypes.

In our sample apps, we’ve only dealt with 3 basic datatypes and one variation:

CHAR/VARCHAR, NUMBER and DATE/DATETIME. We didn’t do any advanced

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PART II: PERSISTENCE APIS AND FRAMEWORKS

COMING SOON IN VOLUME II

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PART III: ENTERPRISE APPLICATION ARCHITECTURE

CONSIDERATIONS

COMING SOON IN VOLUME III

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Stay tuned at www.JavaWebDB.com for updates, new editions,

articles, FAQs and commentary.

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