examples: Examples of .htaccess and README.md

examples/README.md

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+# Examples
+
+This permanent W3ID is meant to be a place to host examples for publishing things on w3id.org.
+
+* [.htaccess](#htaccess)
+  * [What is .htaccess?](#what-is-htaccess)
+  * [Put ID info and maintainer info inside .htaccess](#put-id-info-and-maintainer-info-inside-htaccess)
+  * [Quick intro to URL writing rules](#quick-intro-to-url-rewriting-rules)
+  * [Example 1: Minimalist (grouping)](#example-1-minimalist-grouping)
+  * [Example 2: Supporting multiple media types (MIME types)](#example-2-supporting-multiple-media-types-mime-types)
+  * [Example 3: Dealing with query string](#example-3-dealing-with-query-string)
+* [README.md](#readmemd)
+* [Publish vocabularies with W3ID](#publish-vocabularies-with-w3id)
+
+## .htaccess
+
+`.htaccess` file is the key for the working of URL redirection service of W3ID. Without it, redirection cannot be done.
+
+### What is `.htaccess?`
+
+From [Wikipedia](https://en.wikipedia.org/wiki/.htaccess):
+> An .htaccess (hypertext access) file is a directory-level configuration file
+supported by several web servers, used for configuration of website-access
+issues, such as URL redirection, URL shortening, access control (for different
+web pages and files), and more. The 'dot' (period or full stop) before the
+file name makes it a hidden file in Unix-based environments. 
+
+In W3ID context, it is used primarily for URL redirection. The `.htaccess` file is where you can put URL rewriting rules in. A set of URL rewriting rules will work together and effectively made URL
+redirection happen.
+
+### Put ID info and maintainer info inside .htaccess
+
+You are encouraged to put a breif ID info and a maintainer info in the comment
+(lines staring with `#` character) of a `.htaccess` file.
+
+```ApacheConf
+# Example
+#
+# https://w3id.org/example redirects to https://example.com/
+#
+# ## Contact
+# This space is administered by:  
+#
+# Firstname Secondname
+# email@example.com
+# GitHub username: xxx
+
+RewriteEngine on
+RewriteRule ^ https://example.com/ [R=302,L]
+```
+
+### Quick intro to URL rewriting rules
+
+A simple `.htaccess` file for URL redirection can look like this:
+```ApacheConf
+RewriteEngine on
+RewriteRule ^ https://example.com/ [R=302,L]
+```
+
+`RewriteEngine on` in the first line tells the web server to turn URL rewriting engine on.
+
+While the second line, starting with `RewriteRule`, is the actual rewriting rule.
+
+This is the syntax of the *RewriteRule* directive:
+```ApacheConf
+RewriteRule Pattern Substitution [Flag1,Flag2,Flag3]
+```
+
+* *Pattern* is a Perl compatible regular expression, which means you can specify a sequence of characters to match pattern in the URL.
+  * For example, `^` matches the beginning of the text, `$` matches the end of the text, `.` matches any single character ("a", "7", or any character, one time), and `*` repeats the previous match zero or more times (so `.*` matches "a", "7", "xyz42", and an empty string).
+  * What this Pattern is compared against varies depending on where the RewriteRule directive is defined. In W3ID context, where a per-directory `.htaccess` is used, if the full requested URL is `https://w3id.org/example/subdir/file.html`, the text to be compared against will be `subdir/file.html`.
+* *Substitution* is the string that replaces the text that was matched by Pattern. It can be part of the URL (URL-path) to be combined with the hostname later or it can be a full URL (absolute URL).
+  * In W3ID context, the Substitution tends to be an absolute URL to an external (non w3id.org) resource.
+* *Flags* set [special actions](https://httpd.apache.org/docs/current/rewrite/flags.html) to be performed. Flags is a comma-separated list, surround by square brackets. They are optional. Common flags include `R` (redirect), `L` (last, stop processing the rule set), and `NE` (no character escape).
+
+So in our first example:
+```ApacheConf
+RewriteRule ^ https://example.com/ [R=302,L]
+```
+It means:
+* *Pattern:* `^` -- if a beginning of a string is found in the requested URL (it will always find, as every string must have a beginning):
+* *Substitution:* `https://example.com/` -- replace the whole URL with https://example.com/
+* *Flag1:* `R=302` -- issue a HTTP redirect, with [status code 302](https://en.wikipedia.org/wiki/List_of_HTTP_status_codes), to the client
+* *Flag2:* `L` -- stop processing the rule set
+
+You can have more than one *RewriteRule* in a single `.htaccess` file.
+
+See [Apache HTTP Server documentation](https://httpd.apache.org/docs/current/rewrite/intro.html) for more details about *RewriteRule*, regular expressions, and other directives.
+
+### Example 1: Minimalist (grouping)
+
+This 3 lines of code from [/mircat/.htaccess](https://github.com/perma-id/w3id.org/blob/master/mircat/.htaccess) redirects `https://w3id.org/mircat/<ANYTHING>` to `https://fairsharing.github.io/mircat/<ANYTHING>`.
+
+The URL rewriting rule for that is:
+```ApacheConf
+RewriteRule ^(.*)$ https://fairsharing.github.io/mircat/$1 [R=302,L]
+```
+
+A sequence of characters matches inside a pair of parentheses, or "grouping", will be put in a computer memory and can be recalled by using a special character `$` followed with a group number (`$1`, `$2`, `$15`). A group number is starting from one.
+
+So in the example above, every characters between the beginning of the string (`^`) and the end of the string (`$`) will be stored in group one and can be recalled by a character sequence `$1`.
+
+If the request URL is `https://w3id.org/mircat/subdir/`, the *Pattern* `^(.*)$` will matched with the whole `subdir/`. As `.*` is inside parentheses, `subdir/` will be stored in group one.
+
+When the *Substitution* `https://fairsharing.github.io/mircat/$1` is evaluated, `$1` will be replaced by `subdir/`, resulting a string `https://fairsharing.github.io/mircat/subdir`. This final string will be used for the redirection.
+
+
+### Example 2: Supporting multiple media types (MIME types)
+
+A web server can be configured to return different media type or file format depends on the client's request or capability.
+
+[/ppop/.htaccess](https://github.com/perma-id/w3id.org/blob/master/ppop/.htaccess) demonstrates the use of `RewriteCond %{HTTP_ACCEPT}` to check which [media types](https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_Types) the client accepts or expects to be returned by the server.
+
+A simplified version of the URL rewriting rules in that file will look like this:
+```ApacheConf
+AddType text/turtle .ttl
+
+RewriteEngine on
+
+# Rewrite rule to serve HTML content
+RewriteCond %{HTTP_ACCEPT} text/html
+RewriteRule ^$ https://protect.oeg.fi.upm.es/ppop/ppop.html [R=303,L]
+
+# Rewrite rule to serve TTL content
+RewriteCond %{HTTP_ACCEPT} text/turtle
+RewriteRule ^$ https://protect.oeg.fi.upm.es/ppop/ppop.ttl [R=303,L]
+```
+
+The rule set utilizes the *RewriteCond* directive, which "defines a rule condition. One or more RewriteCond can precede a RewriteRule directive. The following rule is then only used if both the current state of the URI matches its pattern, and if these conditions are met" ([Apache HTTP Server documentation](https://httpd.apache.org/docs/current/mod/mod_rewrite.html#rewritecond)).
+
+The above example will have this behavior:
+* If `%{HTTP_ACCEPT}` matches `text/html`, the server will return an HTML document (`ppop.html`)
+* If `%{HTTP_ACCEPT}` matches `text/turtle`, the server will return a Turtle document (`ppop.ttl`)
+
+The syntax of `RewriteCond` directive is:
+```ApacheConf
+RewriteCond TestString CondPattern [Flags]
+```
+
+Where *CondPattern* is a regular expresssion to match pattern in *TestString*.
+
+In this case, *TestString* is `%{HTTP_ACCEPT}` which its value is taken from an `Accept` field in the HTTP request header. The `Accept` field can be a string like this:
+
+```HTTP
+Accept: text/html, application/xhtml+xml, application/xml, image/webp
+```
+
+Each media type will be presented, separated by a comma. With that, we can use *CondPattern* to matches media types in this string.
+
+
+#### Example 3: Dealing with query string
+
+Everything after the question mark (`?`) in the URL, but not that `?` itself, is a query string.
+
+For example, for the URL `https://en.wikipedia.org/w/index.php?title=Web`, the query string is `title=Web`.
+
+As the query string is not included in the string that the *Pattern* of *RewriteRule* will compared against, you cannot use *Pattern* to match them.
+
+To find pattern in the query string, use `%{QUERY_STRING}` as a *TestString* in *RewriteCond*.
+
+As an example, if you like to redirect the URL `https://w3id.org/example?a=1&b=2`  to `https://example.com/path/file.php?a=1&b=2`, you can use this set of rules:
+
+```ApacheConf
+RewriteCond %{QUERY_STRING} (.*)
+RewriteRule ^ https://example.com/path/file.php?%1? [R=302,L]
+```
+
+In this example, the *CondPattern* `(.*)` in *RewriteCond* will match every characters in the query string (`a=1&b=2`) and put it in group one. This group one (`%1`) is later used in the *Substitution* of *RewriteRule*.
+
+
+
+Note that the special character to recall groups from *CondPattern* of *RewriteCond* is `%` (unlike the special character to recall groups from *Pattern* of *RewriteRule*, which is `$`).
+
+The character `?` at the end of the *Substitution* of *RewriteRule* tells the server not to pass the query string to the final URL after rewrite.
+
+
+## README.md
+
+Each ID hosted on W3ID is expected to have a file named `README.md` containing an information about the ID itself and an information about the maintainer(s). This can be more elaborate than the information inside `.htaccess`.
+
+The `.md` file extension at the end of the file name indicates that the file uses Markdown markup language for text formatting. You can have tables and images as well, if needed.
+
+GitHub will automatically display the content of a `README.md` to repository visitors.
+
+An example of a good README file: [w3id.org/dggs/README.md](https://github.com/perma-id/w3id.org/blob/master/dggs/README.md)
+
+
+## Publish vocabularies with W3ID
+
+If you plan to publish a vocabulary/ontology with W3ID,
+see https://w3id.org/examples/ontology.

examples/ontology/.htaccess

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+# Example repository
+#
+# This permanent w3id is meant to showcase an example on
+# how to publish vocabularies with W3ID.
+#
+# https://w3id.org/examples/ontology redirects to
+# https://w3id.org/example/
+#
+# ## Contact
+# This space is administered by:  
+#
+# Daniel Garijo
+# GitHub username: dgarijo
+
+RewriteEngine on
+RewriteRule ^ https://w3id.org/example/ [R=303,L]

examples/ontology/README.md

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+## Example repository
+
+This permanent w3id is meant to showcase an example on how to publish vocabularies with w3id.
+
+https://w3id.org/examples/ontology redirects to https://w3id.org/example/
+
+
+Maintainer: Daniel Garijo (@dgarijo)