__NOEDITSECTION__  Derived data  Retrieval of data items {{data |pst2|land area}}, using parameter selection template টেমপ্লেট:Pst2, gives the parameter land area, etc.  For retrieval of more data items it is more efficient to prepare a template for that, to be used as follows:  {{data |template name|..|..|..|..}}  so that this data template needs to be called only once.See the first two rows of the first table in m:Help:Array#Summary of counts for template limits. The default template is টেমপ্লেট:উপাত্ত প্রদর্শন, producing this page.  The four parameters are optional, they are passed on to the prepared template as parameters 2-5.  Special templates: টেমপ্লেট:Linkd - link to article টেমপ্লেট:Poptoday - used above টেমপ্লেট:Popdens - for use on the page List of sovereign states and dependent territories by population density টেমপ্লেট:Poptoday 1 - for use on the page List of countries by population টেমপ্লেট:Popareadens - for use on the page List of countries by population  A parameter being undefined or empty typically means the same, see below. {{data ..|pst2|..}} gives the empty string and the text "{{{..}}}", respectively. Therefore an application checking the parameter has to check both. Checking whether a result is equal to e.g. the text "" cannot be done directly with #ifeq in a template which itself has also a parameter with that name, because if that is defined, there would be a comparison with the value instead of the text itself. Instead, it can be checked whether the first character of the result is "{", e.g.: {{#ifeq:{{padleft:|1|{{data {{{continent}}}|pst2|popinc}}}}|{|..|..}}.   নতুন উপাত্ত টেমপ্লেট তৈরি  টেমপ্লেট:Data/preload can be used to create new data templates. On the page of the data template of a province, if there is no data template yet for the country, a link appears to create that, preloading this template. Otherwise the wikitext can be copied to the new data template. For parameters which are not applicable, such as country for a country, the parameter definition "country=" can be deleted. For parameters to be filled in later the parameter definition like "popinc=" (specifying the empty string as value) can be left in the wikitext to be filled in later. Do not forget parameter 1.  Efficiency In this template system each template contains various properties of a single entity, as opposed to the other common system, where a template contains one property (e.g. population or area) of many entities. Although that other system can be convenient if updates of a property for all these entities become available together, in the case of large-scale use of data on one page that other system can be problematic due to its inefficiency. This is because of the following: There are often more entities than properties, and page counts (or in the case of #switch, average page counts) are proportional to the number of data items in the data template (if they are stored in a linear way, not in a tree, and not stored as unnamed parameters). In the case of large-scale use of data on one page there are usually one or more tables, where an entity  forms a row and a property a column, because there are often more entities than properties, and because this way the sorting feature allows sorting entities based on a property. In this template system this allows producing a row with only one call of the data template, making the count not grow faster than proportional to the average number of data items stored per data template, times the number of entities in the table.  The include part of the data template of an entity does not contain a long list of its sub-entities or their properties, because that would make this method inefficient too.    উপরোক্ত নথি টেমপ্লেট:উপাত্ত প্রদর্শন থেকে স্বয়ংক্রিয়ভাবে উৎপন্ন হয়েছে।  }}বিষয়শ্রেণী:উইকিউপাত্ত থেকে উপাত্ত ব্যবহারকৃত টেমপ্লেট বিষয়শ্রেণী:উপাত্ত উদ্ধার টেমপ্লেট