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...

Conclusions

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

Thunderbird 52.3.0 - Email client from M...
As of July 2012, Thunderbird has transitioned to a new governance model, with new features being developed by the broader free software and open source community, and security fixes and improvements... Read more
coconutBattery 3.6.3 - Displays info abo...
With coconutBattery you're always aware of your current battery health. It shows you live information about your battery such as how often it was charged and how is the current maximum capacity in... Read more
Little Snitch 4.0.2 - Alerts you about o...
Little Snitch gives you control over your private outgoing data. Track background activity As soon as your computer connects to the Internet, applications often have permission to send any... Read more
VueScan 9.5.82 - Scanner software with a...
VueScan is a scanning program that works with most high-quality flatbed and film scanners to produce scans that have excellent color fidelity and color balance. VueScan is easy to use, and has... Read more
Postbox 5.0.17 - Powerful and flexible e...
Postbox is a new email application that helps you organize your work life and get stuff done. It has all the elegance and simplicity of Apple Mail, but with more power and flexibility to manage even... Read more
CleanMyMac 3.8.6 - $39.95
CleanMyMac makes space for the things you love. Sporting a range of ingenious new features, CleanMyMac lets you safely and intelligently scan and clean your entire system, delete large, unused files... Read more
Default Folder X 5.1.6b3 - Enhances Open...
Default Folder X attaches a toolbar to the right side of the Open and Save dialogs in any OS X-native application. The toolbar gives you fast access to various folders and commands. You just click on... Read more
Amazon Chime 4.6.5852 - Amazon-based com...
Amazon Chime is a communications service that transforms online meetings with a secure, easy-to-use application that you can trust. Amazon Chime works seamlessly across your devices so that you can... Read more
VOX 2.8.30 - Music player that supports...
VOX just sounds better! The beauty is in its simplicity, yet behind the minimal exterior lies a powerful music player with a ton of features and support for all audio formats you should ever need.... Read more
iFFmpeg 6.4.3 - Convert multimedia files...
iFFmpeg is a comprehensive media tool to convert movie, audio and media files between formats. The FFmpeg command line instructions can be very hard to master/understand, so iFFmpeg does all the hard... Read more

War Wings beginner's guide - how to...
War Wings is the newest project from well-established game maker Miniclip. It's a World War II aerial dogfighting game with loads of different airplane models to unlock and battle. The game offers plenty of single player and multiplayer action. We... | Read more »
How to win every 2v2 battle in Clash Roy...
2v2 is coming back to Clash Royale in a big way. Although it's only been available for temporary periods of time, 2v2 has seen a hugely positive fan response, with players clamoring for more team-based gameplay. Soon we'll get yet another taste of... | Read more »
Roll to Win with Game of Dice’s new upda...
Joycity’s hit Game of Dice gets a big new update this week, introducing new maps, mechanics, and even costumes. The update sets players loose on an exciting new map, The Cursed Tower, that allows folks to use special Runes mid-match. If you feel... | Read more »
Bottom of the 9th (Games)
Bottom of the 9th 1.0.1 Device: iOS iPhone Category: Games Price: $4.99, Version: 1.0.1 (iTunes) Description: Play the most exciting moment of baseball in this fast-paced dice and card game! | Read more »
The best apps for viewing the solar ecli...
If you somehow missed the news, many parts of the United States will be witness to a total solar eclipse on August 21 for the first time in over 90 years. It'll be possible to see the eclipse in at least some capacity throughout the continental U... | Read more »
The 5 best mobile survival games
Games like ARK: Survival Evolved and Conan Exiles have taken the world of gaming by storm. The market is now flooded with hardcore survival games that send players off into the game's world with nothing but maybe the clothes on their back. Never... | Read more »
Portal Walk (Games)
Portal Walk 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Portal Walk is adventure and relaxing platform game about Eugene. Eugene stuck between worlds and trying to find way back home.... | Read more »
Technobabylon (Games)
Technobabylon 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: City of Newton, 2087. Genetic engineering is the norm, the addictive Trance has replaced almost any need for human interaction,... | Read more »
5 reasons why 2v2 is the best mode in Cl...
Supercell has been teasing fans with 2v2 windows that allow players to team up for limited periods of time. The Summer of 2v2 was just this past July, but players are already clamoring for more of that sweet, sweet team-based action. The fans have... | Read more »
The best deals on the App Store this wee...
It seems like the week's only just started, and yet here we are with a huge pile of discounted games to sort through. There are some real doozies on sale this week. We're talking some truly stellar titles. Let's take a look at four of the best... | Read more »

Price Scanner via MacPrices.net

Back To School With The Edge Desk All-in-one...
Back to school is just around the corner, and the ergonomically correct Edge Desk all-in-one portable kneeling desk is ideal for students living in dorms and small apartments, Edge Desk features:... Read more
Norton Core Secure Wi-Fi Router Now Available...
First introduced at the 2017 Consumer Electronics Show (CES), Norton Core, a secure, high-performance Wi-Fi router, fundamentally changed the concept of Wi-Fi routers by making security the primary... Read more
ViewSonic Adds New 27-inch 4K UHD Monitor to...
ViewSonic Corp. has introduced the VP2785-4K, a 27-inch 4K UHD (3840×2160) monitor that delivers precise and consistent color representation and performance to ensure incredible image quality. Built... Read more
Apple now offering Certified Refurbished 2017...
Apple is now offering Certified Refurbished 2017 27″ iMacs for up to $350 off original MSRP. Apple’s one-year warranty is standard, and shipping is free. The following models are available: – 27″ 3.... Read more
13-inch 2.3GHz MacBook Pros on sale for $100...
Amazon has the new 2017 13″ 2.3GHz MacBook Pros on sale today for $100 off MSRP, each including free shipping: – 13″ 2.3GHz/128GB Space Gray MacBook Pro (MPXQ2LL/A): $1199.99 $100 off MSRP – 13″ 2.... Read more
Clearance 2016 13-inch MacBook Airs available...
B&H Photo has clearance 2016 13″ MacBook Airs available for up to $200 off original MSRP. Shipping is free, and B&H charges NY & NJ sales tax only: – 13″ 1.6GHz/128GB MacBook Air (MMGF2LL... Read more
Clearance 21-inch and 27-inch iMacs available...
B&H Photo has clearance 21″ and 27″ Apple iMacs available for up to $500 off original MSRP, each including free shipping plus NY & NJ sales tax only: – 27″ 3.3GHz iMac 5K: $1799 $500 off... Read more
New iOS 11 Productivity Features Welcome But...
The iOS community is in late summer holding mode awaiting the September arrival of the iPhone 8 and iOS 11. iOS 11 public betas have been available for months — number six was released this week —... Read more
Samsung Electronics Launches New Portable SSD...
Samsung Electronics America, Inc. has announced the launch of Samsung Portable SSD T5 – its newest portable solid state drive (PSSD) that raises the bar for the performance of external memory... Read more
TrendForce Reports YoY Gain of 3.6% for 2Q17...
Market research firm TrendForce reports that the global notebook shipments for this second quarter registered a sequential quarterly increase of 5.7% and a year-on-year increase of 3.6%, totaling 39.... Read more

Jobs Board

Business Development Manager - *Apple* Medi...
Job Summary Apple Music is a single, intuitive app that...- all in one place. You can stream any Apple Music song, playlist or album, and download it 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
Frameworks Engineering Manager, *Apple* Wat...
Frameworks Engineering Manager, Apple Watch Job Number: 41632321 Santa Clara Valley, California, United States Posted: Jun. 15, 2017 Weekly Hours: 40.00 Job Summary Read more
Program Manager, *Apple* Pay Business Opera...
…Manager to deliver and sustain a seamless user and support experience for Apple Pay Cash, the upcoming person-to-person payments feature in iMessage. On the Business Read more
Sr. Software Engineer, Core Services, *Apple...
…You will be part of the server team that powers various features within the Apple client applications - iTunes, App Store, iBooks, Podcast, Apple Music etc. You Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.