TweetFollow Us on Twitter

IAC in Sys 7
Volume Number:5
Issue Number:8
Column Tag:Developer's Notes

Related Info: Apple Event Mgr PPC ToolBox Event Manager Edition Manager

Apple's IAC in System 7

By Frank Alviani, Contributing Editor, Waukegan, IL

Inter-Application Communications - The Future is Rapidly Approaching

It was just one year ago that my first article on Inter-Application Communications was printed here in MacTutor. In it and the succeeding two articles Paul Snively and I described and implemented a facility for allowing programs to be written that could automatically communicate without bothering the user. Apple has “validated” that concept by making it a centerpiece of the upcoming System 7.0. This article will be a short look at the approach taken by Apple, and how it is going to change the face of the Macintosh forever. (If you work in Word 4.0 with Superpaint 1.1MS, the linked combination gives some hint of the feel of the linked-document future we are heading towards!) It is NOT an introduction to the actual programming interfaces.

In addition to the new world Apple is entering, DEC has an analogous concept called Compound Data Architecture (CDA). The similarities between a suite of IAC-linked documents on a Mac and a DEC compound document are enough to strongly suggest that once both are established in the marketplace, it will be reasonably straightforward to convert between the two systems. This is a non-trivial operational concern in mixed shops, and important from a marketing viewpoint. I would be mildly surprised if the two companies didn’t work together to ensure the interconvertability of their systems.

Apple has taken a layered approach to implementing their IAC facilities; this is consistent with the approach taken with the other toolboxes and a natural division based on the intended usage for each layer. The material that appeared here in MacTutor corresponds to the PPC-toolbox level in the Apple scheme.

Figure 1 shows the layering designed by Apple, intended to show how interfaces on one layer depend on the next layer down, and how the interfaces at the same level serve different aspects of a common requirement.

SuperPaint!Me:Write Ups:Apple-IAC Illustrations!Draw(107,129:203,179)

SuperPaint!Me:Write Ups:Apple-IAC Illustrations!Draw(103,56:350,178)

The PPC Toolbox

The lowest level provides the raw messaging tools: direct communication and “store and forward”. This level is not intended for user-interface usage. It corresponds most closely to the SAWS IAC system, although the details of the Apple implementation haven’t been spelled out enough to tell how similar the internals are (I suspect they are significantly different, since certain of our IAC facilities are placed in different layers in the Apple software).

This level services two classes of clients: the upper layer of the IAC system software, and non-event based “chunks o’ code” such as RDEVs, DAs, etc. In a sense, all code executing on a Macintosh will be on an equal footing, able to talk with any other code executing at the same time or in the future. It is very important to note that programs and processes do NOT have to be on the same machine to take advantage of the PPC facilities.

These tools open up various interesting possibilities:

• Programs would be able to preserve “state information” across sessions by using the store-and-forward facilities to send messages to their future incarnations.

• Cooperation between programs on networked machines - well beyond the capabilities of today’s programs such as Timbuktu - becomes practical. For example, an artist can be building an illustration for an article, on machine A, while the article is being written on machine B, and the illustration would be in place in the article even while being drawn. This could allow unprecedented cooperation.

• Control panel devices could be used to actually control executing programs, etc. For example, an intercom is one possible such device.

The “Higher Level Events”

For the programmer, there is a significant extension of the event manager: “higher level events”. This is intended mostly for “below the surface” program-to-program requests, many in the form of remote menu-command executions.

In order for higher level events to be extensible for the future, several fields in the existing message record have had additional usages layered on top of their existing definition (in much the same way that the Text Edit toolbox was extended).

As shown in Figure 2, the “message” and “where” fields are redefined when interpreting a higher level event. The “what2” field - message class - identifies the protocol that defines how the specific message in the “what3” field is to be interpreted. How are those message classes going to be assigned so there won’t be anarchy and inadvertent duplication?

Apple long ago put a workable system in place when it decided to use 4 character fields to identify resources, application signatures, etc., and that same system will be used here. Applications will use their signature (‘MACA’, etc.) as the message class they send; Apple is, as usual, reserving all-lower-case combinations for themselves. For each class of messages, there are 232 possible messages.

I expect that at first each publisher will independently define sets of messages that will allow his applications to cooperate. However, there was discussion at the developers’ conference of perhaps arranging a conference on AppleLink to support the growth of a set of industry standard, publisher-independent messages. This would be of enormous benefit to the user, since it would make the development of a universal scripting language (see the note about AppleScript later) much more likely.

Apple will define the message class roughly corresponding to the File and Edit menus (calling their protocol AppleEvents™ and using the signature ‘stdr’); the remaining classes are defined at the discretion of the developers.

The general method of using higher level events is the same that’s used for existing events - WaitNextEvent to accept events and PostEvent to send them. There are few options that don’t exist in System 6, but they don’t change current fundamental techniques.

Certain aspects of this API are still not completely worked out, and will require considerable care to do properly. For example, we now have the possibility of an entirely new class of VandalWare: programs maliciously misusing higher level events. Methods for assuring you are certain of who’s sending a message before you act upon it will be required.

The Publish-and-Subscribe Interface

The segment of most interest to the user is the “publish-and-subscribe” support intended to standardize the user-interface approach. This resembles the technique used in the SAWS IAC driver, and in fact some of the terminology is the same.

The phrase “publish-and-subscribe” was carefully chosen to suggest to users that there can be a slight delay between when data is published and when it is received; it also suggests that there can be geographic separation between the data source and destination.

Apple’s goals for the interface are as follows:

• It must be generalizable - usable for all applications

• It must be scalable - capable of dealing with large amounts of data (for database or multimedia work, for example)

• It must work cleanly with the existing Mac interface

• It must work over the network to support networked cooperative tasks.

Like the SAWS IAC suggested interface, the fundamental units that are linked are sections, not documents. A document can have any number of publishing sections and subscribing sections, and can in fact even subscribe to itself (a wonderful fractal demo took advantage of this fact!) The IAC toolbox called the Publication Manager includes support for resources that are required to track the status of these sections, thus simplifying the programming task. The sections drawn during the demos at the developers’ conference were all rectangular, but I don’t believe that is required (if it is it should be generalized).

Like the SAWS IAC driver, the Apple IAC support can be viewed as an extension of the scrap manager (which is in fact shown in Figure 2). This suggests that applications need the same types of facilities to support IAC - such as the ability to handle at least the standard data formats, such as PICT and TEXT. This minimal level of support alone can go a long way towards making sure that relatively arbitrary combinations of applications can be “integrated” smoothly; your application doesn’t need to know how to interpret every data format in the new universe to fit in.

Unlike the SAWS IAC driver, the published data is kept by Apple in external files. These “pub files” are standard, named files that have their own Finder icon. This approach provides considerably greater generality: by putting “pub files” on a file server such as AppleShare, any number of documents can subscribe to the same data. As with the SAWS IAC driver, the exchange of data from publisher to subscriber can be asynchronous. The System 7.0 enhancements to the file manager provide file-ID facilities that are location-independent, so that publication files can be moved around on a single volume without confusing the client (publisher and subscriber) applications.

Unlike the suggested user interface for the SAWS IAC driver, Apple’s interface explicitly requires intervention for data to be published; the suggested action is when the Save command is invoked. Subscribers in open documents are notified immediately; subscribers in closed documents are notified when that document is next opened. Explicit intervention was chosen to simplify the application’s programming model and to avoid problematic recursive situations. My experience in writing the original MacTutor sample program suggests that this is a good solution; deciding automatically when the fresh data is cooked enough to publish is trickier than it looks, and depends a good deal on the type of data being manipulated. My only suggested extension would be to also have an explicit “update publication” command as an alternative for programs where saving is a time-consuming operation, such as databases.

The subscriber, in the Apple model, is a somewhat passive participant; it normally will just display the data retrieved from the pub file. The user interface guidelines, however, do support the idea of adornment - style changes made to text, etc. by the subscribing application before displaying the new data. Scaling and clipping would be among the appropriate adornments to apply to graphic data.

A very useful facility available to a subscriber is “go to publisher”, possible because of the backlinks between files. Implemented according to the guidelines, this transfers control to the publishing application, after the document has been opened if necessary, and the section has been scrolled into view.

Establishing a linkage between two documents is straightforward:

• The user selects some data; the application calls the publication manager to create the section-tracking resource.

• The “publish” command is invoked. The application brings up a standard-file like dialog to name the “pub file”, and then creates it.

• The user goes to the destination document.

• A section is selected to be a subscriber; the application calls the publication manager to create the section-tracking resource.

• The “subscribe” command is invoked. The application brings up a standard-file like dialog to select the “pub file”, and then reads it.

• The link is established.

Again, the API is not finalized and there are rough edges that will need to be smoothed out before System 7.0 is unleashed on the world. For example, there is no record of the last time a pub file was used, so that there is no easy way to detect “stale” pub files. If you think junk files accumulate on your hard disk, with only you living there, think of what some poor AppleShare administrator is looking at...


The design of the IAC support in System 7.0 was very well done. It will be a reasonable task to incorporate IAC support into existing applications; interface decisions may be more work for some applications than the actual coding. The facilities possible are exciting even to jaded developers - the IAC session kept being interrupted by applause!

In the long run, for anything more complex than a letter to Aunt Sybil, suites of linked documents are going to become the norm due to the convenience of working with your personal favorites in each required specialty. This reduces somewhat the attraction of all-in-one programs such as Lotus’ Jazz and Microsoft Works, although it may prove that requiring no configuration at all is enough of a feature to support a worthwhile market.

Applescript is a nebulous future concept that kept surfacing during the developers’ conference without ever being clearly defined. It sounds like Apple’s syntactic Holy Grail - a single language syntax that is usable for MPW scripts, SADE scripts, and the user’s control of the machine as a whole. One planned feature appears to be that it will have facilities for users to send “higher level event” messages to programs. This would give them text-based application-independent macro capabilities, rather like Tempo.

As an example of what all of these facilities together promise, imagine you have investments in several high-tech stocks that tend to move wildly all over the chart. Keeping peace in the house requires that you prepare a chart every so often to prove that poverty isn’t just around the corner, and so you decide to automate the process to make it less of a nuisance. All it requires is a quick script that does the following:

• At midnight on the 1st of each month, launch your favorite telecomm program with a program to dial up your data service and download all the prices required.

• Launch your wordprocessor with the basic stock report ready to go, including the subscribers for the data values and chart of price gyrations.

• Launch your spreadsheet with a worksheet and macro that loads the new data and charts it. Both the data cells and the chart are publishers, so you save the worksheet and publish the selected data and chart.

• The stock report updated automatically, so just order it to be saved and printed.

• Close all the applications.

MacTutor programmers, of course, will almost instantly be creating scripts of far greater complexity, and there will no doubt be a column devoted to AppleScript programming, but this gives you some idea of the potential that will be available to us in the near future.

In a couple of years we will probably be working in an environment that has some characteristics of the traditional mini-computer: (1) Multiple “parallel” processes, with communications between them, and (2) At least 1 powerful scripting language that allows flexible automation of repetitive actions - but with the addition of almost universal data-interchange formats, a huge variety of off-the-shelf software, and a consistent user interface.

The change from single-program to multi-program workstyle is not going to be without experimental evolution unprecedented in computer history; we’ve never had enough power available on a widespread basis to make this new mode of working feasible. There will undoubtedly be several styles of integration at first, until the market determines which is most workable, for example. There may be conflicts for a while between message sets that make it a little rocky to integrate arbitrary combinations of applications. In spite of these caveats, I am looking forward eagerly to an IACed universe - and so should you.


Community Search:
MacTech Search:

Software Updates via MacUpdate

Civilization VI 1.0.0 - Next iteration o...
Sid Meier’s Civilization VI is the next entry in the popular Civilization franchise. Originally created by legendary game designer Sid Meier, Civilization is a strategy game in which you attempt to... Read more
Paperless 2.3.7 - $49.95
Paperless is a digital documents manager. Remember when everyone talked about how we would soon be a paperless society? Now it seems like we use paper more than ever. Let's face it - we need and we... Read more
Apple iMovie 10.1.3 - Edit personal vide...
With an all-new design, Apple iMovie lets you enjoy your videos like never before. Browse your clips more easily, instantly share your favorite moments, and create beautiful HD movies and Hollywood-... Read more
Apple Numbers 4.0.5 - Apple's sprea...
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
Xcode 8.1 - Integrated development envir...
Xcode includes everything developers need to create great applications for Mac, iPhone, iPad, and Apple Watch. Xcode provides developers a unified workflow for user interface design, coding, testing... Read more
iShowU Instant 1.1.0 - Full-featured scr...
iShowU Instant gives you real-time screen recording like you've never seen before! It is the fastest, most feature-filled real-time screen capture tool from shinywhitebox yet. All of the features you... Read more
RestoreMeNot 2.0.4 - Disable window rest...
RestoreMeNot provides a simple way to disable the window restoration for individual applications so that you can fine-tune this behavior to suit your needs. Please note that RestoreMeNot is designed... Read more
DEVONthink Pro 2.9.6 - Knowledge base, i...
DEVONthink Pro is your essential assistant for today's world, where almost everything is digital. From shopping receipts to important research papers, your life often fills your hard drive in the... Read more
Apple Pages 6.0.5 - Apple's word pr...
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
Safari Technology Preview 10.1 - The new...
Safari Technology Preview contains the most recent additions and improvements to WebKit and the latest advances in Safari web technologies. And once installed, you will receive notifications of... Read more

Latest Forum Discussions

See All

The 4 best food delivery apps
As the temperatures continue to drop, so does the motivation to venture outside. Sometimes you still want to eat a nice meal from that sushi place down the road though. Thankfully in these trying times, there are a number of fine food delivery... | Read more »
Toca Life: Farm (Education)
Toca Life: Farm 1.0 Device: iOS Universal Category: Education Price: $2.99, Version: 1.0 (iTunes) Description: Work and play the farmer's way! Milk your cow, gather eggs from your hens and raise your crops. Have a picnic, play the... | Read more »
The Lost Shield (Games)
The Lost Shield 1.0.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0.0 (iTunes) Description: The Lost shield is a brick break/adventure game. You play as a hero who must return a powerful but dangerous magic shield... | Read more »
The Forgotten Room (Games)
The Forgotten Room 1.0.1 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0.1 (iTunes) Description: Play as paranormal investigator John “Buster of Ghosts” Murr as he explores yet another mysteriously creepy house. This... | Read more »
5 Halloween mobile games for wimps
If you're anything like me, horror games are a great way to have nightly nightmares for the next decade or three. They're off limits, but perhaps you want to get in on the Halloween celebrations in some way. Fortunately not all Halloween themed... | Read more »
The 5 scariest mobile games
It's the most wonderful time of the year for people who enjoy scaring themselves silly with haunted houses, movies, video games, and what have you. Mobile might not be the first platform you'd turn to for quality scares, but rest assured there are... | Read more »
Lifeline: Flatline (Games)
Lifeline: Flatline 1.0.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0.0 (iTunes) Description: The Lifeline series takes a terrifying turn in this interactive horror experience. Every decision you make could help... | Read more »
Game of Dice is now available on Faceboo...
After celebrating its anniversary in style with a brand new update, there’s even more excitement in store for Game of Dice has after just being launched on Facebook Gameroom. A relatively new platform, Facebook Gameroom has been designed for PC... | Read more »
4 addictive clicker games like Best Fien...
Clickers are passive games that take advantage of basic human psychology to suck you in, and they're totally unashamed of that. As long as you're aware that this game has been created to take hold of your brain and leave you perfectly content to... | Read more »
Smile Inc. Guide: How not to die on the...
As if Mondays weren't bad enough, at Smile Inc. you have to deal with giant killer donuts, massive hungry staplers, and blasting zones. It's not exactly a happy, thriving work environment. In fact, you'll be lucky to survive the nine to five.... | Read more »

Price Scanner via

Apple Unveils Redesigned MacBook Pro With Tou...
October 27, 2016 – Apple today introduced the thinnest and lightest MacBook Pro yet, along with a new interface innovation that replaces the traditional row of function keys with a Retina-quality... Read more
Apple Unveils New TV App for Apple TV, iPhone...
October 27, 2016 – Apple today introduced a new TV app, offering a unified experience for discovering and accessing TV shows and movies from multiple apps on Apple TV, iPhone and iPad. The TV app... Read more
Price drops on select refurbished 2015 13″ Re...
Apple dropped prices on select Certified Refurbished 2015 13″ Retina MacBook Pros by as much as $90. An Apple one-year warranty is included with each model, and shipping is free: - 13″ 2.7GHz/256GB... Read more
Apple reveals new next-generation 15″ and 13″...
Apple today revealed their next-generation 15″ and 13″ MacBook Pros. The new models are thinner and lighter than before with a new aluminum design featuring an enhanced keyboard with retina, multi-... Read more
Worldwide Smartphone Shipments Up 1.0% Year o...
According to preliminary results from the International Data Corporation (IDC) Worldwide Quarterly Mobile Phone Tracker, vendors shipped a total of 362.9 million smartphones worldwide in the third... Read more
TuneBand Arm Band For iPhone 7 and 7 Plus Rel...
Grantwood Technology has added the TuneBand for iPhone 7 and 7 Plus to its smartphone armband series. The TuneBand provides a lightweight and comfortable way to wear the iPhone while running,... Read more
1.4GHz Mac mini on sale for $449, save $50
Adorama has the 1.4GHz Mac mini on sale for $50 off MSRP including free shipping plus NY & NJ sales tax only: - 1.4GHz Mac mini (Apple sku# MGEM2LL/A): $449 $50 off MSRP To purchase a mini at... Read more
21-inch 1.6GHz iMac on sale for $999, save $1...
B&H has the 21″ 1.6GHz Apple iMac on sale for $999 including free shipping plus NY sales tax only. Their price is $100 off MSRP. Read more
Macs’ Superior Enterprise Deployment Cost Eco...
IBM’s debunking of conventional wisdom and popular mythology about the relative cost of using Apple Mac computers as opposed to PCs running Microsoft Windows at the sixth annual Jamf Nation User... Read more
12-inch WiFi Apple iPad Pros on sale for $50-...
B&H Photo has 12″ WiFi Apple iPad Pros on sale for $50-$70 off MSRP, each including free shipping. B&H charges sales tax in NY only: - 12″ Space Gray 32GB WiFi iPad Pro: $749 $50 off MSRP -... 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
Software Engineering Intern: UI Applications...
Job Summary Apple is currently seeking enthusiastic interns who can work full-time for a minimum of 12-weeks between Fall 2015 and Summer 2016. Our software Read more
Security Data Analyst - *Apple* Information...
…data sources need to be collected to allow Information Security to better protect Apple employees and customers from a wide range of threats.Act as the subject Read more
*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* Solutions Consultant - Apple (United...
# Apple Solutions Consultant Job Number: 52812872 Houston, Texas, United States Posted: Oct. 18, 2016 Weekly Hours: 40.00 **Job Summary** As an Apple Solutions Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.