TweetFollow Us on Twitter

January 93 - Persistent Objects and Object-Oriented Databases for C++

Persistent Objects and Object-Oriented Databases for C++

Dirk Bartels and Jonathan Robie

Reprinted with permission from C++ Report September 1992. Copyright© 1992 SIGS Publications, 588 Broadway, NY, NY; 212/274-0640; 212/274-0646 (fax).

Many programmers first learn about object-oriented programming by buying a C++ compiler and a GUI class library. These libraries are generally well structured, support true object-oriented design and offer a simple, powerful programming interface. This is often enough to convince programmers to use true object-oriented designs. Unfortunately, many of these programmers find themselves tearing their designs apart when they integrate their programs with conventional database systems, which provide almost no support for objects or for expressing the relationships among objects.

Conventional databases are good at managing large amounts of data, sharing data among programs, and fast value-based queries. They are not very good at modeling the relationships among data, however, since everything must be represented as series of a two-dimensional tables.

Object-oriented database systems (OODBS) are a relatively new tool for software developers. Unlike relational and table-oriented systems, they provide full support for the object-oriented programming model used in languages like C++ and Smalltalk. This model is intuitive, good at modeling relationships, and very suitable for large software projects.

An object-oriented database combines the semantics of an object-oriented programming language with the data management and query facilities of a conventional database system. This makes it easy to manage large amounts of data and to model the relationships among the data. If an object-oriented database is integrated with an object-oriented language, it should support the semantics of that language; relationships established in the program should automatically be represented in the database when objects are stored.

This article focuses on the advantages of object-oriented databases over conventional table-oriented and relational databases and the integration of an OODBS into C++. For small applications these advantages mean that your program will be less complex and easier to understand. For large or complex applications these advantages may mean the difference between success and failure.

LIMITS OF CONVENTIONAL DATABASE SYSTEMS

Database systems are designed for managing large amounts of data, and they provide many important features that object-oriented programming languages do not: permanent storage, fast queries, sharing of objects among programs, device independent formats, and sophisticated error handling for database operations.

Relational database systems (RDBS) and table-oriented systems based on B-Tree or Indexed Sequential Access Method (ISAM) are the standard systems currently used in most software development. Each requires that all data be portrayed as a series of two-dimensional tables. The relational model declares the structures, operations, and design principles to be used with these tables.

These systems are quite appropriate for some applications and were a real breakthrough in their time, but software developers are rapidly learning that life is not a series of two-dimensional tables. The growing complexity of modern programs and the increasing use of dynamic data models have pushed traditional databases to their limit. The limited data models they support can result in significant software development costs since they do not allow program designs that closely match the problem domain. They are not even worth considering for some application areas like computer-aided design (CAD), computer-aided engineering (CAE), multimedia, and office automation.

Limited Data Types

Modern software systems often contain data types that are not easily modeled using such predeclared types. For example, a CAD program might have an array of shapes, or a desktop publishing program might model a page as a series of frames which may contain bitmaps, paragraphs, or vector drawings. We have already seen that object-oriented programs allow us to declare new data types as needed.

Conventional databases have a fixed set of data types. The better systems include both simple data types like INTEGER, FLOAT, or CHAR and complex data types like DATE, TIME, or CURRENCY. New data types cannot be added by the user. If your database does not have the data type you need then you are stuck. Aggregate data types like arrays are rarely available. The only way to group data is to put it in a table.

Limited Modeling of Data Relationships

In conventional database systems, each item is represented as a row in a table. Tables may be accessed sequentially or by searching for values. The only way to express relationships among items is by setting values in the rows. In each table one or more columns is chosen as the primary key; this key must be unique for each row in the table. For instance, the primary keys for a student, a teacher, and a class might each be represented as identification numbers.

The relational model is weak when showing many-to-one relationships, which generally require the introduction of a new table. In our example, the only way to show which students are taking a class is to create an "enrollment" table which has a row for each student and contains the student identification number and class identification number in each row.

Since relational databases have no concept of hierarchy, it is difficult to model the ISA relationship. Suppose we have a "people" table, a "students" table, and a "teachers" table. Every student is also a person, and some of his fields are in each table. To update all of a student's information you must find the rows of each table whose identification numbers match. Every level in the hierarchy requires a new table, and every program using the database must update every relevant table appropriately. The hierarchy is not explicitly represented in the database; you simply have to know why the various tables are there.

No Way of Grouping Code With Data

We have already seen that object-oriented programming languages allow related code and data to be combined to form objects. There is no way to do this in a conventional database system. If you know the name of a table you may use it, and the system will not prevent you from changing the wrong table. As long as you have the right password everything in the database is globally accessible to all of your code.

Limited Manipulation of Data

Database languages are often very poor at manipulating data. SQL, for instance, does not allow you to perform computations on your data as input to a query, nor does it allow you to perform computations on the result of a query. A computer language designer would say that SQL is not computationally complete even though it is relationally complete; a normal human being might say that SQL is great for searching but lousy for anything else. Because of this, most serious applications are written in conventional programming languages using some kind of SQL-based interface to the database.

Poor Integration

Since the database and the host programming language use two different models and different data types the programmer must either perform all operations directly in the database or constantly convert between the two systems. The first method does not let the programmer use many features of the host language; the second means a great deal of overhead and frustration since the relationships among data must be constantly converted to support both programming models. Such a program has two distinct designs, one for the program itself and one for the database.

Summary

To store data in a conventional database, it must be dissected into a series of two-dimensional tables. Only predeclared data types are supported. Object-oriented programming languages have a rich set of features for creating data types and representing the relationships among data that are not supported in such databases. In the rest of this article, we discuss features that an object-oriented database must support. To illustrate these features, we examine POET, a commercial object-oriented database system with which we are connected.

POET
Persistence

The original implementation of Smalltalk had a simple method for storing objects: the program's entire memory image could be dumped to disk and restored when running the program later. This scheme has some real advantages. It is very simple to implement, requires almost no effort from the programmer, and fully implements all aspects of the programming language (after all, the program sticks everything in memory somewhere!). It also has some real disadvantages. The number of objects that can be stored depends on the amount of main memory available, the programming context must be stored and retrieved as a whole, objects may not be shared among programs or retrieved on another kind of computer, and there is no way to implement intelligent error recovery.
 
AAPL
$100.53
Apple Inc.
-0.05
MSFT
$45.43
Microsoft Corpora
+0.21
GOOG
$581.70
Google Inc.
-1.67

MacTech Search:
Community Search:

Software Updates via MacUpdate

calibre 2.0.0 - Complete e-library manag...
Calibre is a complete e-book library manager. Organize your collection, convert your books to multiple formats, and sync with all of your devices. Let Calibre be your multi-tasking digital... Read more
OpenOffice 4.1.1 - Free and open-source...
OpenOffice.org is both an Open Source product and a project. The product is a multi-platform office productivity suite. It includes the key desktop applications, such as a word processor,... Read more
Pages 5.2.2 - Apple's word processo...
Apple Pages is a powerful word processor that gives you everything you need to create documents that look beautiful. And read beautifully. It lets you work seamlessly between Mac and iOS devices. And... Read more
Quicken 2015 2.0.1 - Complete personal f...
The new Quicken 2015 helps you manage all your personal finances in one place, so you can see where you're spending and where you can save. Quicken automatically categorizes your financial... Read more
CleanMyMac 2.2.7 - Delete files that was...
CleanMyMac makes space for the things you love. Sporting a range of ingenious new features, CleanMyMac 2 lets you safely and intelligently scan and clean your entire system, delete large, unused... Read more
MacFamilyTree 7.2.4 - Create and explore...
MacFamilyTree gives genealogy a facelift: it's modern, interactive, incredibly fast, and easy to use. We're convinced that generations of chroniclers would have loved to trade in their genealogy... Read more
Videobox 4.1.1 - Download Flash video th...
Videobox allows you to quickly and easily download Flash video from most all of the popular video sites on the internet. Videobox will convert the video into a native Quicktime format so it's ready... Read more
Web Snapper 3.3.5 - Capture entire Web p...
Web Snapper lets you capture Web pages exactly as they appear in your browser. You can send them to a file as images or vector-based, multi-page PDFs. It captures the whole Web page - eliminating... Read more
Picasa 3.9.138 - Organize, edit, and sha...
Picasa and Picasa Web Albums allows you to organize, edit, and upload your photos to the Web from your computer in quick, simple steps. Arrange your photos into folders and albums and erase their... Read more
Tidy Up 3.0.15.0 - Find duplicate files...
Tidy Up is a complete duplicate finder and disk-tidiness utility. With Tidy Up you can search for duplicate files and packages by the owner application, content, type, creator, extension, time... Read more

Latest Forum Discussions

See All

Doctor Who: Legacy Review
Doctor Who: Legacy Review By Jennifer Allen on August 22nd, 2014 Our Rating: :: RUN OF THE MILLUniversal App - Designed for iPhone and iPad Doctor Who: Legacy is an ok match-3 puzzle game, but it lacks some much needed personality... | Read more »
Pentumble (Games)
Pentumble 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: *** Special Launch Price! 33% Off! *** Pentumble combines the joy of a free-flowing platformer with beautiful graphics and levels... | Read more »
DotEmu Summer Sale Cuts Several Games’ P...
DotEmu Summer Sale Cuts Several Games’ Prices to $0.99 Posted by Ellis Spice on August 21st, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
King Announces its Newest “Saga” – Diamo...
King Announces its Newest “Saga” – Diamond Digger Saga Posted by Jessica Fisher on August 21st, 2014 [ permalink ] Diamond Digger Saga, by King Digital Entertainment, promises to be another addictive, adorable game in the “Saga” | Read more »
Spacetime Studios’ Greg Mueller Tells Al...
| Read more »
TourStar Review
TourStar Review By Rob Thomas on August 21st, 2014 Our Rating: :: BORING TOURINGUniversal App - Designed for iPhone and iPad When The Ramones sang “Touring, touring/It’s never boring,” they clearly weren’t referring to TourStar.... | Read more »
Track Your Pregnancy with Glow Nurture
Track Your Pregnancy with Glow Nurture Posted by Jessica Fisher on August 21st, 2014 [ permalink ] iPhone App - Designed for the iPhone, compatible with the iPad | Read more »
Repel the advances of aliens and space...
King’s Empire developer Tap4Fun has a whole catalogue of games under its belt, including a space-based role-playing title called Galaxy Legend. Set in the 2841, Galaxy Legend follows humanity as it begins to expand to the furthest stars in the... | Read more »
Outcast Odyssey – An Interview with the...
At this year’s San Diego Comic-Con, fans got the chance to meet and mingle with several of the artists behind Magic Pixel Games and Namco Bandai’s upcoming card battler, Outcast Odyssey. Considering many of these artists have worked on comics in the... | Read more »
Hanx Writer Review
Hanx Writer Review By Jennifer Allen on August 21st, 2014 Our Rating: :: NOSTALGIC WRITINGiPad Only App - Designed for the iPad Miss writing on a typewriter? Hanx Writer replicates that experience pretty well on your iPad.   | Read more »

Price Scanner via MacPrices.net

Leftover 15-inch 2.0GHz Retina MacBook Pros a...
B&H Photo has leftover previous-generation 15″ 2.0GHz Retina MacBook Pros now available for $1599 including free shipping plus NY sales tax only. Their price is $400 off original MSRP. B&H... Read more
Pro.Calendar – New Productivity App for iPad...
Austin, Texas based mobile business and productivity app developer LightArrow, Inc. has announced Pro.Calendar, a powerful and intuitive calendar app with eight versatile calendar options including... Read more
SanDisk Ultra II SSD — Supercharge Your Syste...
SanDisk Corporation has announced the new SanDisk Ultra II SSD with enhanced SSD Dashboard. The new drive is designed to deliver a cost-effective and easy upgrade solution for PC owners looking to... Read more
Samsung and Barnes & Noble Introduce New...
Samsung Electronics America and NOOK Media, a subsidiary of Barnes & Noble, Inc. have announced the introduction of the new Samsung Galaxy Tab 4 NOOK, a 7-inch tablet combining Samsung’s leading... Read more
21-inch iMacs on sale for up to $150 off MSRP
B&H Photo has 21″ iMacs on sale for up to $150 off MSRP including free shipping plus NY sales tax only. B&H will also include a free copy of Parallels Desktop software: - 21″ 2.7GHz iMac: $... Read more
27-inch 3.2GHz iMac on sale for $1698, save $...
Abt has the 27″ 3.2GHz iMac on sale for $1698 including free shipping. Their price is $101 off MSRP. Read more
Mac Backup Guru 2.0 Drive Backup/Cloneing Uti...
Mac Backup Guru developer MacDaddy has released Mac Backup Guru 2.0, offering new and enhanced advanced features, such as bootable backups, synchronised volumes and folders, and a Snapshot mode that... Read more
Operate GE’s New Free-Standing KItchen Range...
Think you accidentally left the oven on? Switch it off while on the go. The new free-standing Profile™ Series gas and electric ranges are GE’s second cooking appliances, following their wall oven, to... Read more
Parallels Announces Parallels Desktop 10 for...
The no. 1-selling software for running Windows applications on a Mac becomes an even easier choice for millions of consumers and IT professionals worldwide with the launch of the most powerful... Read more
Apple now offering certified refurbished 2014...
 The Apple Store is now offering Apple Certified Refurbished 2014 MacBook Airs for up to $180 off the cost of new models. An Apple one-year warranty is included with each MacBook, and shipping is... Read more

Jobs Board

*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
Position Opening at *Apple* - Apple (United...
**Job Summary** As more and more people discover Apple , they visit our stores seeking ways to incorporate our products into their lives. It's your job, as a Store Read more
Position Opening at *Apple* - Apple (United...
…Summary** As a Specialist, you help create the energy and excitement around Apple products, providing the right solutions and getting products into customers' hands. You Read more
Project Manager, *Apple* Financial Services...
**Job Summary** Apple Financial Services (AFS) offers consumers, businesses and educational institutions ways to finance Apple purchases. We work with national and Read more
*Apple* Solutions Consultant (ASC)- Retail S...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.