follow the XLink specification. The schema must ultimately extend the XBRL instance schema document and typically extend other published XBRL schemas on the xbrl.org website. Taxonomy schemas define Item and Tuple "concepts" using <xsd:element> elements. Concepts provide names for the fact and indicate whether or not it is a tuple or an item, the data type (such as monetary, numeric, fractional, or textual), and potentially more metadata. Items and Tuples can be regarded as "implementations" of concepts, or specific instances of a concept. A good analogy for those familiar with object oriented programming would be that Concepts are the classes and Items and Tuples are Object instances of those classes. This is the source of the use of the "XBRL instance" terminology. In addition to defining concepts, taxonomy schemas reference linkbase documents. Tuples instances are 1..n relationships with their parents; their metadata is simply the collection of their attributes. Linkbases are a collection of Links, which themselves are a collection of locators, arcs, and potentially resources. Locators are elements that essentially reference a concept and provide an arbitrary label for it. In turn, arcs are elements indicating that a concept links to another concept by referencing the labels defined by the locators. Some arcs link concepts to other concepts. Other arcs link concepts to resources, the most common of which are human-readable labels for the concepts. The XBRL 2.1 specification defines five different kinds of linkbases. Label Linkbase Reference Linkbase Calculation Linkbase Definition Linkbase Presentation Linkbase Label Linkbase This linkbase provides human readable strings for concepts. Using the label linkbase, multiple languages can be supported, as well as multiple strings within each language. XBRL aims to become a worldwide standard for electronic business reporting. This requires taxonomies to present business data in many different languages. Therefore, it is important to be able to create an element that is assigned with labels for different languages. There may also be different labels for different purposes. All labels are stored and linked to the elements in a label linkbase. Elements defined in a schema are built to convey accounting meaning to computers. In order to make it easier for computers to process their names, they have to obey some rules. For example, the use of spaces is not allowed so 'Cash and Cash Equivalents' would be named 'CashAndCashEquivalents' . Additionally, big taxonomies such as IFRS obey specific rules of naming and labelling to