Contemporary Publishing Technology Essentials (2)

SGML and PDF, why both of us need (below)
(SGML and PDF—Why We Need Both)

Three, about PDF
When SGML evolved as the most powerful information exchange technology, Adobe Systems developed another kind of exchange technology, PDF, which is a completely different approach. In fact, the original PDF was only a subsidiary technology of Adobe Acrobat. Acroba and SGML produce the same purpose, but SGML mainly serves the "mainstream world", that is, large companies, large organizations, while Acroba is to meet the needs of individual PC users, used to exchange documents with customers, suppliers and other partners.

(1) PDF, shared page form instead of information and structure With Acrobat, using Word software to generate files on Mac machines, you can use Word Perfect to run the resulting Acrobat page on your PC. SGML thinks the best way is to let The file recipient decides how to run and format these files according to their own environment. Adobe believes that the document is sent out in the hope that the recipient sees the same file as the one it was originally created on—page by page, line by line, word-by-word, and includes all graphs, tables, equations, blanks, and For all colors, in order to achieve this, Adobe continues to bring Acrobat affiliate technology PDF, which is a byproduct of Postscript. In the graphical world, Postscript is the standard way of describing electronic pages, but there is a fundamental difference between Postscript and PDF. Postscript is a programming language and PDF is a page description format.

As a programming language, Postscript is very powerful, it can fully explain various applications, and can also generate visual pages in various ways. However, when reading Postscript files, they can only be sorted from beginning to end, because a program description on the first page may still be useful on page 51. Therefore, you cannot extract the 51th page and read it separately.

And PDF is different. As a page description format, each page is independent, because PDF gives all the information needed to display this page, because it does not need to be as complex computer selection as Postscript, the PDF code must be consistent And much more predictable. When the pages are generated by Quark, Penta, PageMaker, and Xyvision several different systems, Postscript describes them quite differently, and the resulting PDF format is basically similar.

The reason for this consistency in PDF is that a Postscript conversion called Distiuer has a very standard PDF page description.

(b) The presentation form of the page The PDF format contains all the information needed to describe the final representation of the page. If the recipient's computer has the required font, he will use it directly. If not, he will use the two fonts on the host to replace the original font. This effect is sometimes unsatisfactory, so it is best to use the required font. Nested within the resulting PDF format.

In addition to fonts, PDF also includes all other visual elements, such as: blanks, graphics, colors, layout layout, etc. Since PDF is a vector technology, the text graphics effect of the PDF file will be adjusted accordingly to the output device. The resolution standard shows a resolution of 72 dpi on the screen, 300 or 600 dpi when printed with a laser printer, and up to 2540 dpi with a high-resolution imagesetter.

(B) PDF: Visual Communication Structure In SGML, the structural features that people are accustomed to being translated into the logical structure of the computer language are not so intuitive. Many people who have written DTDs for SGML files will feel that some of the structural relationships were originally known on the page, but it would be too much trouble to describe them in words, and they would have to face many ambiguous questions. The square brackets and the square Brackets, usage is consistent? May be a summary of one finger, an excerpt of one finger, then how to distinguish? This must be a thorough and detailed analysis of the document.

In contrast, PDF has no such trouble because PDF is a visual communication structure. On the PDF page, all the structural features are directly represented. For example, the first-level title is much more obvious than the second-level title. The footnotes are placed in the bottom corner of the page. In the text, a certain data or chart will appear immediately after the text... And many of these structural features have been established in the traditional media, and readers can see at a glance. This point is very attractive to publishers who pay attention to the form of the page.

(3) PDF: The standard format of printing, Acrobat, brings these advantages to the field of printing. In fact, soon the printer chose PDF to replace PostScrip. There are many reasons for this: First, the PDF file is less troublesome when it is delivered to the printing, because the Dfistiuer program will prompt potential problems with the file, such as lost fonts, images, etc. Secondly, for pages with complex images, PDF files are much smaller than the corresponding PostScript. Thirdly, there is another important reason why each page of PDF is independent, then it is possible to divide all the pages into multiple groups and deal with them in parallel. Adobe's Extreme technology works like this, dividing PDF files into multiple sets of file streams. By using multiple RIPs (the Raster Image Processer) to convert the PS or PDF code into black and white dots for printing, simultaneous processing is performed, which greatly reduces the working time. PostScrip's latest version, PostScrip3, allows

PDFs are processed directly in RIP without first converting to PostScript, which was required in previous versions.

For these reasons, printers have found that PDFs are the most efficient format for printing typographic pages regardless of whether they are output from digital printers such as laser printers, typesetting machines, or DocuTech.

(d) With PDF, why use SGML?
Since the PDF is so simple for electronic publishing and is the standard format for printing, why use SGML? A very intuitive reason is that the format of printed pages rarely works well on the screen, so the need to reformat the page to fit the needs of the screen display is obviously inconvenient. If you use SGML, it will be much easier.

The more important reason is that PDF contains too little structural information, and Acrobat also provides some navigation features: Thumbhail Views, bookmark is easy to generate, full text can be indexed by Acrobat's Catalog software, all PDF files can be searched by Boolean, and even You can create hyperlinks between Acrobat files, but these tasks are usually done manually. If you have more work, the cost is too high. However, some of the metadata provided by PDF, such as keywords, modification dates, author names, etc., are usually ignored because they cannot be generated automatically.

Since the essential difference between SGML and PDF is that SGML is about structure, and PDF is about page description, both are largely complementary. The disadvantages of the PDF mentioned above are being compensated by SGML. Therefore, with PDF, it is still necessary to use SGML.

(E) PDF is a proprietary technology PDF and SGML have another key difference. SGML is an independent, universal standard, and PDF is an exclusivity standard. SGML can be used on any platform through any software. While PDF is developed and owned by Adobe Corporation, PDF pages must be browsed by Adobe's Acrobat Reader software (V is for free in this software and applies to Macitosh, Windows and Unix systems); to generate PDF files through PostScrip to purchase Acrobat Distiller is used as part of a stand-alone program or other application; to generate a book mark, plug-in hyperlinks require Acrobat Catalog, and so on. Although the above software is reasonably priced and simple to use, it is not as free as SGML.

After the description (PDF), it is necessary to point out that the structure provided by SGML is necessary. Many journal publishers have experience. PDF is the best form of providing electronic pages to subscribers. However, these pages are often accompanied by SGML titles to navigate and help readers find the pages they want to see. Even without the SGML title, there will be HTML or XML marked "Click Here, Download PDF", and the best source for these HTML and XML is the SGML archive.

I. Conclusion: Where are the SGML and PDF used? Looking at the above, you can clearly understand the advantages of SGML and PDF, and you will not think that they are in conflict with each other. Instead, they complement each other and have their own use. Here's a summary of where they are used.

SGML:
1. If you plan a series of books or journals that are clearly structured and repeatable, use SGML. Although there will be a lot of work in the first book or journal, once such a structured workflow is formed, the subsequent work is basically repetitive, thus reducing costs.

2. If you plan to publish in a variety of media, such as printing, CD-ROM, Web, etc., please use SGML, because it can greatly reduce the conversion work between media, thereby reducing costs.

PDF:
1. If you want to generate a layout page, use PDF. It can send books and periodical pages to the printer. It can facilitate the electronic transfer of proofs. It also provides Internet users with a layout page for browsing or local printing. The best form.
2. If you only make CD-ROM publications, choose PDF, which requires additional work and little cost, and is the most economical and effective way.

Note: More information about SGML and PDF is available on the following websites. About PDF The most complete, up-to-date information

The best source of SGL related information

The best source of XML related information