TweetFollow Us on Twitter

Text-based File Formats

Volume Number: 19 (2003)
Issue Number: 2
Column Tag: Section 7

Text-based File Formats

CSV, OML, XML, YAML...

by Rich Morin

BSD and OSX inherit a long tradition (stretching back into the earliest days of Unix) of using text files for data storage. Although there are some exceptions, most control, log, and other system data files are written in ASCII. This makes them easier to inspect, post-process, and even edit.

Apple, whose historic bent has been more toward binary file formats (e.g., the resource fork), seems to have adopted this idea wholeheartedly. In fact, they have gone a bit further, adopting XML (rather than line-oriented files) and Unicode (rather than ASCII). As a result, many OSX files are well structured, language-independent, and quite accessible to both humans and programs.

Many vendors (e.g., Microsoft) are also joining the XML caravan. Assuming that they document both the syntax and semantics of their interchange formats, we could see a dramatic change in possibilities for file interchange.

It is not clear, however, that XML is the Right Answer for all problems. Let's look at some of the alternatives, examining their strengths and weaknesses. Don't expect a comprehensive list; there are zillions of data formats in use. Here, in any event, are some that I would recommend.

CSV

Although CSV stands for "comma-separated values", commas are by no means essential to the idea. In fact, another term for this is "flat file format". Basically, the idea is that each line is a record and that some other delimiter (e.g., colons, commas, white space) is used to separate fields. Quotes or other devices are sometimes used to protect instances of the delimiter in the body of a field. Here are some examples:

/etc/crontab
  15 3 * * * root periodic daily
/etc/gettytab
  a|std.110|110-baud:\
        :np:nd#1:cd#1:uc:sp#110:
/var/log/netinfo.log
  Dec 21 17:59:33 cerberus netinfod ...
An_Excel_File.csv
  1,2,3
  "1,2,3","3,4,5"

Some files get a bit complex, adding syntax to support block structure, comments, line breaks, shell commands, etc. A highly-ornamented CSV file can begin to look like a "little language". Here is a fairly complex format, drawn from /var/named/named.local:

$TTL 86400
@ IN SOA localhost. root.localhost. (
    1997022700 ; Serial
    28800      ; Refresh
    14400      ; Retry
    3600000    ; Expire
    86400 )    ; Minimum
  IN NS  localhost.
1 IN PTR localhost.

Many BSD control files, logs, and reports use white space to delineate fields, making the assumption that the included data will not contain spaces. This was never a safe assumption for path names, but the advent of OSX has made the problem all too real.

Try running "ps -axww" and see how man path names (for both commands and arguments) contain spaces. Then, consider how you would code up a way to determine which spaces are field separators and which are not. Not simple...

Of course, ps has other problems. Run "vi 1 '2 3' 4" in one window and "ps" in another. In the ps output, the COMMAND field looks like "vi 1 2 3 4", dooming any effort to parse it into a command path and distinct command-line arguments. Some sort of quoting convention is desperately needed here.

Blanks in path names make it impossible to parse certain log files, have already broken one Apple installer script, and could well foul up many BSD control files. It's probably too late to get Apple to back off from their use of embedded blanks in system path names, so you can expect to see some problems of this nature coming along...

OML

Although CSV is attractively simple, it may be too simple for your needs. For instance, you may need to support optional data, hierarchical structures, etc. On the other hand, you may not be ready for the formality of XML (Extensible Markup Language) and unwilling to design your own markup language (and parser).

OML (Ostensible Markup Language :-) is a powerful, simple, and convenient solution to this dilemma:

# This is a sample of file-system metadata.
<snap>
  <file>ASCII text</>
  <flags>f,avbstclinmed,,</>
  <lstat>303507,33200,1,1000,20,914,8</>
  <md5>2e1240f444fc3f984186fc5a4fd28eb0</>
  <times>1040087752,230,1740993,10890145</>
</snap>

This looks quite a bit like XML, but there are some small peculiarities. That comment, for instance, isn't legal XML. Nor is "</>" a legal termination for a tag. Is that really CSV syntax in the middle of some fields? Finally, where are the header lines?

Though OML is seemingly designed to give hives to XML purists, it is also designed to work smoothly with existing XML tools. A couple of lines of Perl will strip out the comments and fill out the terminations. A quick pass through an XML parser extracts all of the named fields and attributes. Perl's split() operator, if need be, can break up the CSV data.

Since OML is pretty much a "roll your own" kind of thing, there isn't any real documentation. I'd suggest a look at "Doing it Simpler" (Leigh Dodds; www.xml.com) for some ideas, however.

XML

Despite any appearance to the contrary, I am quite a fan of XML. An enormous amount of meticulous and thoughtful effort (and some rather fancy computer science!) is going into creating "industrial strength" data formats and processing tools. In addition, the W3C (World Wide Web Consortium; www.w3.org) is being very careful to make sure that the official standards are open to all players.

For some projects, you really need to bring in power tools. The host of translators, validators, and other tools that XML provides can make otherwise impossible projects feasible, if not necessarily reasonable. Using XML also increases the chance that someone else's program will be able to parse your data. Given all of that, complaining about a bit of formality seems rather petty.

I won't try to cover XML here; there are shelves of books on the subject, with more coming out on a weekly basis. O'Reilly and Addison-Wesley have the broadest coverage; O'Reilly's XML web site (www.xml.com) is a good place to start your journey...

YAML

CSV has low overhead, is simple to read and edit, and handles lists and arrays well. OML and XML are a bit more bulky, but handle optional data and hierarchies smoothly. XML has an impressive suite of documentation, standards activities, and support software. Sometimes, however, you want low overhead, simplicity, and support for arbitrary data structures.

YAML (YAML Ain't Markup Language) fills this niche quite admirably. The syntax is simple and clean. The basic data structures are sequences (i.e., Perl arrays) and mappings (i.e., Perl hashes). YAML handles lists, arrays, and hierarchies easily; with a bit of extra work, it can handle arbitrary Perl data structures (e.g., cyclic graphs).

Here is the previous example, transliterated into YAML:

# This is a sample of file-system metadata.
snap:
  file:  'ASCII text'
  flags: 'f,avbstclinmed,,'
  lstat: '303507,33200,1,1000,20,914,8'
  md5:   '2e1240f444fc3f984186fc5a4fd28eb0'
  times: '1040087752,230,1740993,10890145'

A more idiomatic rendering, however, would look like:

# This is a sample of file-system metadata.
snap:
  file:  ASCII text
  flags: [ f, avbstclinmed, , ]
  lstat: [ 303507, 33200, 1, 1000, 20, 914, 8 ]
  md5:   2e1240f444fc3f984186fc5a4fd28eb0
  times: [ 1040087752, 230, 1740993, 10890145 ]

Aside from the fact that some spaces have been added after commas and the quotes have been eliminated (some turned into brackets), the second version looks very similar to the first. The resulting data structure is quite different, however; the bracketed lists have been turned into YAML sequences. This means that they don't have to be parsed in a follow-on step. Here is some access code, in Perl:

$file = $yaml{snap}{file};
$uid  = $yaml{snap}{lstat}[3];

YAML has several ways to write textual data. Here are some examples:

  - a simple text item
  - "double-quoted text\n "
  - 'single-quoted text'
- >
    This text
    is freeform.
- |
    This text
    isn't.

Although YAML has nowhere near the amount of documentation that XML has, there are some useful resources to recommend. The YAML web site (www.yaml.org) is the logical place to start; be sure to visit the YAML wiki. I'd also recommend a look at "Look Ma, No Tags" (Kendall Clark Grant; www.xml.com) for an informal introduction.


Rich Morin has been using computers since 1970, Unix since 1983, and Mac-based Unix since 1986 (when he helped Apple create A/UX 1.0). When he isn't writing this column, Rich runs Prime Time Freeware (www.ptf.com), a publisher of books and CD-ROMs for the Free and Open Source software community. Feel free to write to Rich at rdm@ptf.com.

 
AAPL
$105.22
Apple Inc.
+0.39
MSFT
$46.13
Microsoft Corpora
+1.11
GOOG
$539.78
Google Inc.
-4.20

MacTech Search:
Community Search:

Software Updates via MacUpdate

Ember 1.8.2 - Versatile digital scrapboo...
Ember (formerly LittleSnapper) is your digital scrapbook of things that inspire you: websites, photos, apps or other things. Just drag in images that you want to keep, organize them into relevant... Read more
Tonality Pro 1.1.2 - Professional-grade...
Tonality Pro gives you the power to create stunning and dramatic black & white images. This is a complete monochrome image editor with more than 150 one-click style presets, totally unique... Read more
VueScan 9.4.49 - 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
OS X Server 4.0 - For OS X 10.10 Yosemit...
Designed for OS X and iOS devices, OS X Server makes it easy to share files, schedule meetings, synchronize contacts, develop software, host your own website, publish wikis, configure Mac, iPhone,... Read more
TotalFinder 1.6.12 - Adds tabs, hotkeys,...
TotalFinder is a universally acclaimed navigational companion for your Mac. Enhance your Mac's Finder with features so smart and convenient, you won't believe you ever lived without them. Tab-based... Read more
BusyCal 2.6.3 - Powerful calendar app wi...
BusyCal is an award-winning desktop calendar that combines personal productivity features for individuals with powerful calendar sharing capabilities for families and workgroups. BusyCal's unique... Read more
calibre 2.7 - Complete e-library managem...
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
Skitch 2.7.3 - Take screenshots, annotat...
With Skitch, taking, annotating, and sharing screenshots or images is as fun as it is simple.Communicate and collaborate with images using Skitch and its intuitive, engaging drawing and annotating... Read more
Delicious Library 3.3.2 - Import, browse...
Delicious Library allows you to import, browse, and share all your books, movies, music, and video games with Delicious Library. Run your very own library from your home or office using our... Read more
Art Text 2.4.8 - Create high quality hea...
Art Text is an OS X application for creating high quality textual graphics, headings, logos, icons, Web site elements, and buttons. Thanks to multi-layer support, creating complex graphics is no... Read more

Latest Forum Discussions

See All

Rami Ismail Opens Up distribute​() for D...
Rami Ismail Opens Up distribute​() for Developers Posted by Jessica Fisher on October 24th, 2014 [ permalink ] Rami Ismail, Chief Executive of Business and Development at indie game studio | Read more »
Great Hitman GO Goes on Sale and Gets Ne...
Great Hitman GO Goes on Sale and Gets New Update – Say That Three Times Fast Posted by Jessica Fisher on October 24th, 2014 [ permalink ] | Read more »
Rival Stars Basketball Review
Rival Stars Basketball Review By Jennifer Allen on October 24th, 2014 Our Rating: :: RESTRICTIVE BUT FUNUniversal App - Designed for iPhone and iPad Rival Stars Basketball is a fun mixture of basketball and card collecting but its... | Read more »
Rubicon Development Makes Over a Dozen o...
Rubicon Development Makes Over a Dozen of Their Games Free For This Weekend Only Posted by Jessica Fisher on October 24th, 2014 [ permalink ] | Read more »
I Am Dolphin Review
I Am Dolphin Review By Jennifer Allen on October 24th, 2014 Our Rating: :: NEARLY FIN-TASTICUniversal App - Designed for iPhone and iPad Swim around and eat nearly everything that moves in I Am Dolphin, a fun Ecco-ish kind of game... | Read more »
nPlayer looks to be the ultimate choice...
Developed by Newin Inc, nPlayer may seem like your standard video player – but is aiming to be the best in its field by providing high quality video play performance and support for a huge number of video formats and codecs. User reviews include... | Read more »
Fighting Fantasy: Caverns of the Snow Wi...
Fighting Fantasy: Caverns of the Snow Witch Review By Jennifer Allen on October 24th, 2014 Our Rating: :: CLASSY STORYTELLINGUniversal App - Designed for iPhone and iPad Fighting Fantasy: Caverns of the Snow Witch is a sterling... | Read more »
A Few Days Left (Games)
A Few Days Left 1.01 Device: iOS Universal Category: Games Price: $3.99, Version: 1.01 (iTunes) Description: Screenshots are in compliance to App Store's 4+ age rating! Please see App Preview for real game play! **Important: Make... | Read more »
Toca Boo (Education)
Toca Boo 1.0.2 Device: iOS Universal Category: Education Price: $2.99, Version: 1.0.2 (iTunes) Description: BOO! Did I scare you!? My name is Bonnie and my family loves to spook! Do you want to scare them back? Follow me and I'll... | Read more »
Intuon (Games)
Intuon 1.1 Device: iOS Universal Category: Games Price: $.99, Version: 1.1 (iTunes) Description: Join the battle with your intuition in a new hardcore game Intuon! How well do you trust your intuition? Can you find a needle in a... | Read more »

Price Scanner via MacPrices.net

Weekend sale: 13-inch 128GB MacBook Air for $...
Best Buy has the 2014 13-inch 1.4GHz 128GB MacBook Air on sale for $849.99, or $150 off MSRP, on their online store. Choose free home shipping or free local store pickup (if available). Price valid... Read more
Nimbus Note Cross=Platform Notes Utility
Nimbus Note will make sure you never forget or lose your valuable data again. Create and edit notes, save web pages, screenshots and any other type of data – and share it all with your friends and... Read more
NewerTech’s Snuglet Makes MagSafe 2 Power Con...
NewerTech has introduced the Snuglet, a precision-manufactured ring designed to sit inside your MagSafe 2 connector port, providing a more snug fit to prevent your power cable from unintentional... Read more
Apple Planning To Sacrifice Gross Margins To...
Digitimes Research’s Jim Hsiao says its analysts believe Apple is planning to sacrifice its gross margins to save its tablet business, which has recently fallen into decline. They project that Apple’... Read more
Who’s On Now? – First Instant-Connect Search...
It’s nighttime and your car has broken down on the side of the highway. You need a tow truck right away, so you open an app on your iPhone, search for the closest tow truck and send an instant... Read more
13-inch 2.5GHz MacBook Pro on sale for $949,...
Best Buy has the 13″ 2.5GHz MacBook Pro available for $949.99 on their online store. Choose free shipping or free instant local store pickup (if available). Their price is $150 off MSRP. Price is... Read more
Save up to $125 on Retina MacBook Pros
B&H Photo has the new 2014 13″ and 15″ Retina MacBook Pros on sale for up to $125 off MSRP. Shipping is free, and B&H charges NY sales tax only. They’ll also include free copies of Parallels... Read more
Apple refurbished Time Capsules available sta...
The Apple Store has certified refurbished Time Capsules available for up to $60 off MSRP. Apple’s one-year warranty is included with each Time Capsule, and shipping is free: - 2TB Time Capsule: $255... Read more
Textilus New Word, Notes and PDF Processor fo...
Textilus is new word-crunching, notes, and PDF processor designed exclusively for the iPad. I haven’t had time to thoroughly check it out yet, but it looks great and early reviews are positive.... Read more
WD My Passport Pro Bus-Powered Thunderbolt RA...
WD’s My Passport Pro RAID solution is powered by an integrated Thunderbolt cable for true portability and speeds as high as 233 MB/s. HighlightsOverviewSpecifications Transfer, Back Up And Edit In... Read more

Jobs Board

*Apple* Solutions Consultant - Apple Inc. (U...
…important role that the ASC serves is that of providing an excellent Apple Customer Experience. Responsibilities include: * Promoting Apple products and solutions Read more
Senior Event Manager, *Apple* Retail Market...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global event strategy. Delivering an overarching brand story; in-store, Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**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
Project Manager / Business Analyst, WW *Appl...
…a senior project manager / business analyst to work within our Worldwide Apple Fulfillment Operations and the Business Process Re-engineering team. This role will work Read more
*Apple* Retail - Multiple Positions (US) - A...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.