<aname="repositories"><h3>what is a repository?</h3></a>
<p>A <i>repository</i> is a service in the hydrus network that stores a certain kind of information<6F>files or tag mappings, for instance<63>as submitted by users all over the internet. Those users periodically synchronise with the repository so they know everything that it stores. Sometimes, like with tags, this means creating a complete local copy of everything on the repository. Hydrus network clients never send queries to repositories; they perform queries over their local cache of the repository's data, keeping everything confined to the same computer.</p>
<p>A <i>tag</i> is a small bit of text describing a single property of something. They make searching easy. Good examples are "flower" or "nicolas cage" or "the sopranos" or "2003". By combining several tags together ( e.g. [ 'tiger woods', 'sports illustrated', '2008' ] or [ 'cosplay', 'the legend of zelda' ] ), a huge image collection is reduced to a tiny and easy-to-digest sample.</p>
<li>Although it may seem preferable to have 'The Lord of the Rings' rather than 'the lord of the rings', there are many, many special cases where style guides differ on which words to capitalise.</li>
<li>Searches become far easier when case is not matched. And When case does not matter, what point is there in recording it?</li>
<p>Secondly, leading and trailing whitespace is removed, and multiple whitespace is collapsed to a single character. <pre>' yellow dress '</pre> becomes <pre>'yellow dress'</pre></p>
<aname="namespaces"><h3>what is a namespace?</h3></a>
<p>A <i>namespace</i> is a category that in hydrus prefixes a tag. An example is 'person' in the tag 'person:ron paul'--it lets people and software know that 'ron paul' is a name. You can create any namespace you like; just type one or more words and then a colon, and then the next string of text will have that namespace.</p>
<p>The hydrus client gives namespaces different colours so you can pick out important tags more easily in a large list, and you can also search by a particular namespace, even creating complicated predicates like 'give all files that do not have any character tags', for instance.</p>
<aname="filenames"><h3>why not use existing filenames and folders?</h3></a>
<li>A filename is not guaranteed to stay the same, meaning other programs cannot rely on the filename address being valid or even returning the same data every time.</li>
<li>A filename is often<65>for <i>ridiculous</i> reasons<6E>limited to a certain prohibitive character set. Even when utf-8 is supported, some arbitrary ascii characters are usually not, and different localisations, operating systems and formatting conventions only make it worse.</p>
<li>Folders can offer context, but they are clunky and time-consuming to change. If you put each chapter of a comic in a different folder, for instance, reading several volumes in one sitting can be a pain. Nesting many folders adds navigation-latency and tends to induce less informative "04.jpg"-type filenames.</li>
</ul>
<p>So, the client tracks files by their <i>hash</i>.</p>
<p>Please do not tag your files with their exact original 'filename.jpg' on my public tag repo. <ahref="https://www.youtube.com/watch?v=_yYS0ZZdsnA">Shed the concept of filenames as you would chains.</a></p>
<p>Hashes are a subject you usually has to be a software engineer to find interesting. The simple answer is that they are unique names for things. It can be proven that f099b5823f4e36a4bd6562812582f60e49e818cf445902b504b5533c6a5dad94 refers to one particular file and no other. Hashes make excellent identifiers inside software. In the client's normal operation, you will never encounter a file's hash. If you want to see a thumbnail bigger, double-click it; the software handles the mathematics.</p>
<p><i>For those who </i>are<i> interested: hydrus uses SHA-256, which spits out 32-byte (256-bit) hashes. The software stores the hash densely, as 32 bytes, only encoding it to 64 hex characters when the user views it or copies to clipboard. SHA-256 is not perfect, but it is a great compromise candidate; it is secure for now, it is reasonably fast, it is available for most programming languages, and newer CPUs perform it more efficiently all the time.</i></p>
<p>They are long enough to be impossible to guess, and also randomly generated, so they reveal nothing personally identifying about you. Many people can use the same access key (and hence the same account) on a repository without consequence, although they will have to share bandwidth limits, and if one person screws around and gets the account banned, everyone will lose access.</p>
<p>The access key is the account. Do not give it to anyone you do not want to have access to the account. An administrator will never need it; instead they will want your <i>account key</i>.</p>
<aname="account_keys"><h3>what is an account key?</h3></a>
<p>This is another long string of random hexadecimal that <i>identifies</i> your account without giving away access. If you need to identify yourself to a repository administrator (say, to get your account's permissions modified), you will need to tell them your account key. You can copy it to your clipboard in <i>services->review services</i>.</p>
<p>If an Internet Explorer "Navigation Cancelled" page appears whenever you click on a swf thumbnail, try installing Flash Player for Internet Explorer. Just having it installed for Firefox/Opera is not enough; you need the ActiveX component that comes with the specific IE version. Just boot IE and download/run the installer from Adobe's site.</p>
<aname="delays"><h3>why can my friend not see what I just uploaded?</h3></a>
<p>The repositories do not work like conventional search engines; it takes a short but predictable while for changes to propagate to other users.</p>
<p>The client's searches only ever happen over its local cache of what is on the repository. Any changes you make will be delayed for others until their next update occurs. At the moment, the update period is 100,000 seconds, which is about 1 day and 4 hours.</p>
