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Back to the 5 minute metadata video series in this video were going to to be discussing data dictionaries what they are whats stored in them and what up a good one so the first question is what is a data dictionary. Lets first talk about what other kind of dictionaries. There are the definition of a dictionary is a book listing and explaining the words of a language here ive set up three different kinds of dictionaries.
We have an english dictionary. A german dictionary and a scrabble dictionary. Theyre all dictionaries.
But the context of each is completely different to the next one you want to look up a german word in the english dictionary. The dictionary helps provide the context for words a data dictionary tells us the context of a collection of data lets have a look at what this looks like in practice here we have some information about these three books that i have were going to record down the title. The publisher and the year that the book was published because im only collecting data for a handful of books right.
Theres a lot of space for me to record this information everything can be written out fully. And its easy to understand because its not that much information that had to be recorded. But if you were to collect more information about these books.
There isnt as much space. Anymore so you would have to abbreviate some things and this makes it harder to understand what the columns mean now because of this we now have to record down somewhere what these columns mean and this is what a data dictionary is if a good dictionary has the word and the meaning of that word. What is a good way of recorded in the context of data to start off.
If you would need the name of the column. So we can look it up. We would then need the definition.
So we would know what that column means some other common things you might want to record are the data type.
So we can interpret the information. Appropriately and also the size. So we know how much space it takes up in the database.
And maybe a list of possible values. If there is a list of codes used in that field. These are the most common things you might see.
But there are others that may be more appropriate for your data. Now lets look at some examples to make sense of what im recording i need to build a data dictionary earlier. I drew a table about my dictionaries recording the title publisher year and the number of pages now im going to build a data dictionary that records the context of these columns first lets start off with the title and add the definition.
Which is the title of the dictionary.
This is a straightforward example. But now i dont have to guess what this column. Means now ill make an entry for the publisher.
The publisher is repeated and that takes time to write down because a lot of publishers have long names like the oxford english dictionary. Because of this im going to abbreviate the publishers name this makes the data faster to enter and takes up less space oxford. English dictionary becomes the code oh edie.
But it isnt the only one and i also have to record the code so it gets interpreted correctly if youre going to use codes you need a data dictionary to explain them the codes are still text. But they now have a special meaning. Why is recording the number of pages important well its because i cannot tell what the longest or shortest book is in my collection.
I dont have a lot of room to record information so use three digits to record the number of pages. But what if my book has more than 999 pages in my data. Ill record this as 999 and in my data dictionary.
Ill write this down and tell people that 999 is actually 999 or above. Now. Im going to record the year of publication this looks like a number.
But it cant be treated like one because dates arent numbers you can find the differences between two dates. But you cant add them together because that wouldnt make any sense so now you know what would go into a data dictionary. But in real life you wouldnt record them on a whiteboard youll find them in a word document an excel spreadsheet or an xml file and also in a metadata registry.
But whenever you store data its important to record a data dictionary to make sure people understand the context of your data. Thank you for watching. And be sure to check us out on aristotle metadata com.
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