By B. Douglas Wake and William C. Wake
Summary: Sometimes we have information that is potentially useful or important, but is not normally of interest. This pattern discusses when and how to hide this information in plain sight.
Context
- Information is designed using a high format and a powerful (often new) tool.
- Information is viewed in a low format by a less powerful (often previously existing) tool.
Forces
- Translating from high to low form loses information – we can’t easily translate back from low to high form.
- The high form is retained for future modification.
- The low form may be treated as read-only.
Resolution
“Hide” high-form information in the low-form object, in such a way that the low-form tool or the user can ignore the hidden information.
Discussion
The low form is read-only, because low-level tools will not know enough to manipulate the information in the high form. (If they did, they’d be high-form tools in disguise.) The hidden information need not be a complete replication of all high-form information; it might be just enough information to locate the high-form original.
Examples
- Netscape Navigator. (See http://www.netscape.com). Navigator’s page can be set up to display the URL on the printed page. Then, the printed form is the low form, but it contains the URL that can be used to locate the high form.
- MIME mail. (N. Freed and N. Borenstein, RFC 2045, “Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies,” November, 1996.) The MIME data format allows for complex mail messages that contain alternative formats for a single message. A complete MIME mail reader might support display of all forms of a message. A mail reader with minimal MIME support might display the plain ASCII version of a message, and ignore the other forms. A mail reader unaware of MIME might display all parts of the MIME message (which would include the simple ASCII form).
- Digital watermarks. (Ref??) A museum with images might freely distribute low-resolution versions of its images, including a visible watermark that identifies the source of the image. The museum might sell a high-resolution version containing an invisible watermark that would allow detection of illegal re-distribution of the image.
- XEROX PARC’s XAX system. (W. Johnson et al., “Bridging the paper and electronic worlds: The paper user interface,” Proceedings of INTERCHI, 1993, pp. 507-512, ACM, April, 1993.) The XAX system encodes information about a document in glyphs that are “not visually distracting when embedded in a paper document.” This lets them move from the low-level paper form up to high-level structured electronic forms.
[Originally written November, 1997.]