19.1 Computing overall quality values

As a first step in the local variant selection algorithm, the overall qualities associated with all variant descriptions in the list are computed.

局所変種選択算法の最初の手順として、 目録のすべての変種記述に関連付けられる総合品質を計算します。

The overall quality Q of a variant description is the value

変種記述の総合品質 Q は値

• Q = round5( qs * qt * qc * ql * qf * qa )

where rounds5 is a function which rounds a floating point value to 5 decimal places after the point. It is assumed that the user agent can run on multiple platforms: the rounding function makes the algorithm independent of the exact characteristics of the underlying floating point hardware.

です。ここで、 round5 は小数点以下5桁に浮動小数点値を丸める関数です。 利用者エージェントは複数の環境で実行され得ます。 丸め関数によって算法は浮動小数点ハードウェアの正確な特色とは独立したものとします。

The factors qs, qt, qc, ql, qf, and qa are determined as follows.

因子 qs, qt, qc, ql, qf, qa は次のように決定します。

qs Is the source quality factor in the variant description.

qs

変種記述の原典品質因子。

qt The media type quality factor is 1 if there is no type attribute in the variant description. Otherwise, it is the quality value assigned to this type by the configuration database. If the database does not assign a value, then the factor is 0.

qt

変種記述に型属性がなければ媒体型品質因子は 1。 そうでなければ、設定データベースでこの型に割当てられた品質値。 データベースに値が割当てられていなければ、この因子は 0。

qc The charset quality factor is 1 if there is no charset attribute in the variant description. Otherwise, it is the quality value assigned to this charset by the configuration database. If the database does not assign a value, then the factor is 0.

qc

変種記述に charset 属性がなければ charset 品質因子は 1。 そうでなければ、設定データベースでこの charset に割当てられた品質値。 データベースに値が割当てられていなければ、この因子は 0。

ql The language quality factor is 1 if there is no language attribute in the variant description. Otherwise, it is the highest quality value the configuration database assigns to any of the languages listed in the language attribute. If the database does not assign a value to any of the languages listed, then the factor is 0.

ql

変種記述に言語属性がなければ言語型品質因子は 1。 そうでなければ、設定データベースでこの言語属性に挙げられている言語に割当てられた品質値の最高値。 どの言語もデータベースに値が割当てられていなければ、この因子は 0。

qf The features quality factor is 1 if there is no features attribute in the variant description. Otherwise, it is the quality degradation factor computed for the features attribute using the feature set of the current request.

qf

変種記述に特徴属性がなければ特徴品質因子は 1。 そうでなければ、現在要求の特徴集合を使って特徴属性について計算した品質減衰因子。

qa The quality adjustment factor is 0 if the variant description lists a media type - charset combination which is `forbidden' by the table, and 1 otherwise.

qa

変種記述の媒体型‐charset 組合せが表で「禁止」されているものであれば品質調整因子は 0, そうでなければ 1。

As an example, if a variant list contains the variant description

• {"paper.2" 0.7 {type text/html} {language fr}}

and if the configuration database contains the quality value assignments

• types: text/html;q=1.0, type application/postscript;q=0.8
• languages: en;q=1.0, fr;q=0.5

then the local variant selection algorithm will compute the overall quality for the variant description as follows:

     {"paper.2" 0.7 {type text/html} {language fr}}
                 |           |                 |
                 |           |                 |
                 V           V                 V
       round5 ( 0.7   *     1.0        *      0.5 ) = 0.35000

With same configuration database, the variant list

     {"paper.1" 0.9 {type text/html} {language en}},
     {"paper.2" 0.7 {type text/html} {language fr}},
     {"paper.3" 1.0 {type application/postscript} {language en}}

would yield the following computations:

       round5 ( qs  * qt  * qc  * ql  * qf  * qa ) = Q
                ---   ---   ---   ---   ---   ---
      paper.1:  0.9 * 1.0 * 1.0 * 1.0 * 1.0 * 1.0  = 0.90000
      paper.1:  0.7 * 1.0 * 1.0 * 0.5 * 1.0 * 1.0  = 0.35000
      paper.3:  1.0 * 0.8 * 1.0 * 1.0 * 1.0 * 1.0  = 0.80000

19.2 Determining the result

Using all computed overall quality values, the end result of the local variant selection algorithm is determined as follows.

計算したすべての総合品質値を使って、局所変種選択算法の最終結果を次の通り決定します。

If all overall quality values are 0, then the best variant is the fallback variant, if there is one in the list, else the result is the conclusion that none of the variants are acceptable.

すべての総合品質値が 0 であれば、最善の変種は fallback 変種が目録中にあればその変種で、なければ結果はどの変種も受入れ不能であるとの結論です。

If at least one overall quality value is greater than 0, then the best variant is the variant which has the description with the highest overall quality value, or, if there are multiple variant descriptions which share the highest overall quality value, the variant of the first variant description in the list which has this highest overall quality value.

少なくても1つの総合品質値が 0 より大きければ、 最高の総合品質値の記述のある変種が最善の変種で、 最高の総合品質値の変種記述が複数ある場合は、 そのうちで一番最初に目録で変種記述がある変種が最善の変種です。