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.
 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Opera 47.0.2631.83 - High-performance We...
Opera is a fast and secure browser trusted by millions of users. With the intuitive interface, Speed Dial and visual bookmarks for organizing favorite sites, news feature with fresh, relevant content... Read more
Vivaldi 1.12.955.36 - An advanced browse...
Vivaldi is a browser for our friends. In 1994, two programmers started working on a web browser. Our idea was to make a really fast browser, capable of running on limited hardware, keeping in mind... Read more
Apple Configurator 2.5 - Configure and d...
Apple Configurator makes it easy to deploy iPad, iPhone, iPod touch, and Apple TV devices in your school or business. Use Apple Configurator to quickly configure large numbers of devices connected to... Read more
Smultron 10.0 - Easy-to-use, powerful te...
Smultron 10 is an elegant and powerful text editor that is easy to use. You can use Smultron 10 to create or edit any text document. Everything from a web page, a note or a script to any single piece... Read more
BetterTouchTool 2.304 - Customize multi-...
BetterTouchTool adds many new, fully customizable gestures to the Magic Mouse, Multi-Touch MacBook trackpad, and Magic Trackpad. These gestures are customizable: Magic Mouse: Pinch in / out (zoom... Read more
Drive Genius 5.0.5 - $49.50 (50% off)
Drive Genius features a comprehensive Malware Scan. Automate your malware protection. Protect your investment from any threat. The Malware Scan is part of the automated DrivePulse utility. DrivePulse... Read more
Apple Keynote 7.3 - Apple's present...
Easily create gorgeous presentations with the all-new Keynote, featuring powerful yet easy-to-use tools and dazzling effects that will make you a very hard act to follow. The Theme Chooser lets you... Read more
Apple Numbers 4.3 - Apple's spreads...
With Apple Numbers, sophisticated spreadsheets are just the start. The whole sheet is your canvas. Just add dramatic interactive charts, tables, and images that paint a revealing picture of your data... Read more
Apple Pages 6.3 - Apple's word proc...
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
Smultron 9.4.2 - Easy-to-use, powerful t...
Smultron 9 is an elegant and powerful text editor that is easy to use. Use it to create or edit any text document. Everything from a web page, a note or a script to any single piece of text or code.... Read more

ARise (Games)
ARise 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: **ARKit only Puzzle game****Chapter 1 available now - More worlds coming soon!** ARise is an experience about perspective. Using the AR... | Read more »
The best games to play while you wait fo...
SteamWorld Dig 2 is out this week on PC and Switch, and people are understandably excited. This clever series by Image and Form combines our favorite metroidvania mechanics with an esquisite universe, excellent storytelling, and true wit. While... | Read more »
Drag'n'Boom beginner's gu...
Have you ever wanted to burn and pillage a village as a bloodthirsty dragon? If you answered yes to that question, Drag'n'Boom offers you the perfect chance to do so, casting you as an adorable little dragon that wants to set humankind aflame. It... | Read more »
Thimbleweed Park (Games)
Thimbleweed Park 1.0.0 Device: iOS Universal Category: Games Price: $9.99, Version: 1.0.0 (iTunes) Description: A brand new adventure game from Ron Gilbert and Gary Winnick, creators of the classics Monkey Island and Maniac Mansion!... | Read more »
The best simulation games on mobile
There's nothing like a good sim -- from the seemingly ridiculous to the incredibly mundane, you can be there's a simulation game out there for your every whim. [Read more] | Read more »
INKS guide - how to create works of pinb...
INKS puts a clever new spin on everyone's favorite classic arcade game, pinball. The core mechanics are the same -- keep a little ball pinging around the board for as long as possible without letting it fall into the precarious holes in the board.... | Read more »
Warbands: Bushido (Games)
Warbands: Bushido 1.0 Device: iOS Universal Category: Games Price: $3.99, Version: 1.0 (iTunes) Description: Warbands:Bushido is a miniatures board game with cards, miniatures, dice and beautiful terrains to fight on, with both... | Read more »
The best mobile games like Divinity: Ori...
Divinity: Original Sin 2 launched this week to the excitement of RPG fans everywhere. The game, which derives a lot of of its story and mechanics from old-school isometric RPGs and Dungeons & Dragons, has unseated PlayerUnknown's... | Read more »
Iron Marines guide - beginner tips and t...
Iron Marines is a brilliant RTS title that feels a bit like Starcraft. It's got a sci-fi setting and some of the most spectacular strategy mechanics we've seen in mobile games to date. With that said, the RTS genre can be a bit tricky to break... | Read more »
The best new games we played this week -...
The work week can be tough, but on the bright side, it's almost overandthere are bunches of brand new games to try out this weekend. This week definitely makes up for last week's sleepiness ten-fold. We've got one of the finest RTS game on mobile... | Read more »

Price Scanner via MacPrices.net

Is iPhone X Really The Future Of The Smartpho...
Should iPhone X even be called a telephone? It does of course support telephony and texting, but its main feature set is oriented to other things. It is also debatable whether it makes any rational... Read more
OtterBox Announces Full Case Lineup for iPhon...
Apple revolutionized the smartphone industry 10 years ago with the original iPhone, and OtterBox has set the standard of protection from the very beginning by protecting every generation of iPhone.... Read more
LifeProof Introduces What’s NEXT Cases for iP...
LifeProof built its reputation on sleek, ultra-protective iPhone cases. From 360-degree coverage to the first screenless waterproof case, the protection pioneer has always pushed the limits.... Read more
Apple Refurbished 2016 15-inch MacBook Pros a...
Apple has Certified Refurbished 2016 15″ Touch Bar MacBook Pros available starting at $1949. An Apple one-year warranty is included with each model, and shipping is free: – 15″ 2.7GHz Touch Bar Space... Read more
Wednesday deal: 15-inch MacBook Pros for up t...
B&H Photo has 2017 15″ MacBook Pros on sale for $150-$200 off MSRP. Shipping is free, and B&H charges sales tax in NY & NJ only: – 15″ 2.8GHz MacBook Pro Space Gray: $2199, $200 off MSRP... Read more
2.6GHz Mac mini on sale for $599, $100 off MS...
B&H Photo has the 2.6GHz Mac mini (MGEN2LL/A) on sale for $599 including free shipping plus NY sales tax only. Their price is $100 off MSRP. Read more
Snag a 15-inch 2.2GHz Retina MacBook Pro, App...
Apple has Certified Refurbished 2015 15″ 2.2GHz Retina MacBook Pros available for $1699. That’s $300 off original MSRP, and it’s the lowest price available for a 15″ MacBook Pro currently offered by... Read more
Apple Refurbished 3TB Time Capsule for $279,...
Apple has Certified Refurbished 3TB Time Capsules available for $279 including free shipping plus Apple’s standard one-year warranty. Their price is $120 off MSRP. Read more
19% off Smart Battery Cases for iPhone 7
Amazon has both Black and White Smart Battery Cases for iPhone 7s available for $80.41 including free shipping. Their price is $18.59, or 19%, off MSRP. Read more
Back on sale: 10.5-inch 64GB iPad Pros for $5...
MacMall has 10.5″ 64GB Apple iPad Pros on sale again for $599 including free shipping. That’s $50 off MSRP and the lowest price available for this model from any reseller. Read more

Jobs Board

*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* News Product Marketing Mgr., Publish...
Job Summary The Apple News Product Marketing Manager will work closely with a cross-functional group to assist in defining and marketing new features and services. Read more
Development Operations and Site Reliability E...
Development Operations and Site Reliability Engineer, Apple Payment Gateway Job Number: 57572631 Santa Clara Valley, California, United States Posted: Jul. 27, 2017 Read more
*Apple* Solutions Consultant - Apple Inc. (U...
…about helping others on a team while also delighting customers? As an Apple Solutions Consultant (ASC), you will discover customers needs and help connect them Read more
Software/Data Engineer, *Apple* Media Produ...
Job Summary Apple Media Products is the team behind the App Store, Apple Music, iTunes, and many other high profile products on iPhone, Mac and AppleTV. Our Data Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.