DITA: Database Technologies

Good Evening everyone,

This post is going to be the last as it concerns the Data Information and Technology Architectures coursework.

In the previous post we focused a lot on the method of storing and representing data in computers by using files. But except from this widely known method there is also another one which is more efficient and this is the database approach method. So in this post I am gone mention some characteristics of the database approach method and then I am going to focus on the relational database model and the technologies to retrieve data.

It was the disadvantages of the file approach that pushed the data processing departments of the organisations to find a new method to store and manage large amounts of data. The main disadvantage of the file approach method is the dependence that exists between the data and the programs. Moreover because the data are stored in separate and unrelated files that might even have different format, takes longer to access and retrieve them and often is likely to have data that are being duplicated. These duplicate data except from the fact that capture more space they can also cause problems when it needs to be updated or needs to be retrieved.

On the other hand the database approach is completely different and at the same time much more efficient. The fact that the database approach has a lot more advantages and is more effective from than the file approach is result of the way that the data are being stored and organised.

All data are being gathered in a central and corporate database according to the relationships that might exist between them. There is a Database Management System, also known and as DBMS, that centrally manages all the data in the database. Because of this gathering of the data and also because of the central way that the DBMS manages them is being avoided the appearance of duplicate information. With no duplications, we avoid possible inconsistencies in the data which has as a result the system to be more integral.

The DBMS as we mentioned and to the lecture is a complex piece of software, which acts as the interface between the users and the data. So the information that the data contain is shared between the users that require it and the DBMS allows the users to retrieve only the information that is being related to them. Moreover with the DBMS the security is better from the file method approach, as it concerns accessing the data, because not everyone is allowed to access them. The database has an administrator known as Database Administrator, who allows to users to access or not the data. But the most important thing with the database approach is that the data are independent, so when changes need to be made to the database's applications and mechanisms these changes doesn't affect the data.

In the relational model the data of an application are being represented as a group of relations between the data. In our case the application is a whole database so the relational database is being represented as a collection of two-dimensional tables which is the most common and practical way to express the relations. In order to make this representation more comprehensive we have an example. In the table that follows every row is known as a record and it refers to a unique student.

All these records are composed by a set of attributes which take specific values. These set of attributes in every relational database are composed in a way that we won't have any duplicates. The SSN attribute is an attribute that takes a unique value for each student, so if we know this number we can find any student that we are looking for, this kind of attribute is known as primary key. Every relation has a primary key but in some cases this key might be consisted of more than one attributes (composite foreign key). Apart from the primary key in some relations we might also have foreign keys. These keys are references to other tables. This means that there are relationships that exist between different tables.

But in order to create these tables, which means to start designing the relational database, the best thing that we should do first is to create a diagram known as entity-relationship (ER) diagram for our database. With this type of diagram as we can realize from its name we capture the entities of the database which are the tables/relations that we have already mentioned. But with the diagram we also find the relationships that might exist between the entities. Once we have implemented the ER diagram then we can create our tables in the two-dimensional form, that we have mentioned, and as a result we can create the whole relational database.

The SQL initials stand for Structured Query Language which is the most widely language that is being used to manage Database Management Systems. With the SQL we can create the tables that we have mentioned in a way that the computer systems can understand what they represent. Moreover after having implemented all the tables of the database that the DBMS manages users of the database can use SQL expressions in order to retrieve data that might need, update data that already exist or even add/delete data.

Here I have some examples of how you can create a table in SQL, how you can insert records to this table and of course how you can retrieve data from this kind of tables.

This is an example of how we can create the table of our example

Here is an example of how we can add a record to the table that we have created

With similar way can add as many records to the table as we want

And finally here is an example of how we can retrieve specific data from a table like the one that we have created

In this example we retrieve the values for the Name and the SSN attributes from all Students that exist in our table with the GPA's attribute value being more than 3.5

In conclusion we must say that the database approach has been very useful not only in the computer society but also to everyone that has to do with large amounts of data. The database approach has provided a much more efficient way to organise, store and manage data. This in combination with the relational model and the technologies that "escort" it, it has given to everyone an even more fast and effective way to retrieve data that are important to them.

REFERENCES

1. Andy MacFarlane, Richard Butterworth (2009), "Digital Information Technologies and Architectures", Lecture 7: Structuring and querying information stored in databases, City University.
2. Andy MacFarlane, Jonathan Raper and Jason Dykes (2009), "Information Technologies and Architectures", Lecture 8: Information Retrieval, City University.
3. http://whatis.techtarget.com/
4. http://aetos.it.teithe.gr/~amarg/Databases/Chapter03.pdf
5. http://sqlcourse.com/

DITA: Data Representation and File Formats

Hello again,

This time in our post we will talk about digital organization and digital representation and we also going to mention some things about Metadata and Marking-Up.

101000101010001... No I am not mistaken that is what I wanted to write, but what exactly is this? What it represents?

The most important is who or what will "interpret" it. For a human being this could be a number but for computer systems this could possibly represent something different.

Humans count and generally perform arithmetic by using the base ten number system, which is the most known number system. But except from this system there are also and many others with different bases, and to make it more clear when we mention base we mean the number of different digits that are being used to represent data. In each of these systems we combine the digits in a way that means something to us.

Similar is the way that computer systems work. The computer systems are based on the binary number system, which is consisted of only two digits, zero ("0") and one ("1"). With this specific number system the computer systems organise and represent information/data. Inside the systems a binary digit is represented with an electromagnetic state. Zero means non-positive electromagnetic state and one means positive electromagnetic state. So all the data that

are being stored in computer systems are being stored as binary code (sequences of binary digits) and because of this we often refer to them as digital data.

Each zero and one is known as bit, as sequences of 0 and 1 the computer systems can store in optical or hard disks large amounts of data. A sequence of 8 bits is known as byte (the most known unit of digital information). Every sequence of bits represents something different but something that is very interesting is that if we increase by one bit the sequence of bits then we can represent twice as many values as all the previous sequences can.

As we said the binary system is used to represent, organize, store and send data and when we say data we don't mean only numeric but also alphabetic (text) and alphanumeric data that have a specific purpose. Those data in their binary form are being interpreted from processors, according to appropriate agreed methods of interpretation (file formats), to create characters that are easier for humans to read. The most characteristic examples of character encoding schemes are the ASCII and the Unicode.

All these data is obvious that need to be organised in an efficient way. That's why is being used the concept of the file. "A computer file is a block of arbitrary information, or resource for storing information, which is available to a computer program". The size of a file must be finite. The information that a file contains can consist of smaller pieces of information which can be individually different but will have some common things (certain topic, theme etc.). The advantage of files is that can be manipulated as a single entity and can be grouped into folders which are collections of related information. With the folders we have a hierarchical organization of the files, because each folder can contain sub-folders. In this hierarchy the initial folder that contains all the other sub-folders is called "root". So beginning from the root we can follow a "path" through the sub-folders in order to find the file/s that we are interested in.

We mentioned that through the different file formats that exist we can store in files and textual information. But this information is just simple text without any evidence of how this text that the files contain is going to be displayed, where do we need to emphasize and where we need to use other fonts, generally there isn't any information about how the text should be presented and the semantics of it.

That's where the metadata and the marking-up are very useful. The metadata is data about data, in our case is more information about how the textual context of the file should be interpreted. On the other hand marking-up is the "action" with which we can add metadata on the contents of text files. The marking-up can be done in two different ways, the presentational and the semantic. The former has to do with how the text should be presented and the latter with what the text means. The semantic is the most important of the two because with this marking-up we can understand and process the data in a more efficient way.

So we can understand that is very important if we want to have all these data interpreted we need to know not only the format that those files have but also and the meaning of the marking-up that escorts them.

Summarizing we must say that the digital representation of data was a revolution to the representation of information. As a result now we are able to access as many times as we want any data without being afraid that would be compromised. Also we can easy create as many genuine copies of specific data as we want, transfer them to other computer systems and then by using processors interpret them again. Moreover, because of the digital representation of the data we can use the capabilities of the computers and manage great amounts of information in a more efficient and quick way, having as result the extraction of even more information from the data.

Humans/scientists took advantage, in a good way, of the theory that data have the meaning that people give them and through that they succeeded great things in the "world" of data organization and representation.

REFERENCES

• Richard Butterworth,based on original work by Jason Dykes (2009), "Digital Information Technologies and Architectures", Lecture 2:Digital Reoresentation and Organisation, Meta-Data/Markup, City University
• http://en.wikipedia.org/wiki/Computer_file
• http://whatis.techtarget.com/
• http://en.wikipedia.org/wiki/Byte

DITA: Blog Evaluation

Hello everyone,

Long time long see.

It has been a long time since I last posted something but here I am again.

This time as you can understand I am writing in English and here is the explanation. I would use my blog for the needs of my coursework for the Digital Information Technologies and Architectures module also known as DITA. So this post and a couple more that will follow would have to do with my module.

In this first post I am going to describe my blog, how is organized and also I am going to evaluate it. But before that I think that would be good to mention some fundamental things about blogs.

First of all what is exactly a Blog?

A blog, or Weblog as it is the original name, is a site based on Web 2.0 Technology, this means that the blog has a dynamic content, this content is short pieces of text (mostly known as posts) which are organised by time, with the most recent of the posts being at the top of the central page of the blog. The text is often being "escorted" from embedded videos and photographs which have as result the posts to appear more interesting and at the same time to make the topic of the posts more comprehensible to the visitors of the blog.

The fact that only a specific number of posts can be at the main page of the blog doesn't mean that someone can't access the earlier ones. As it concerns how often posts are being made there is not a particular pattern, this depends on the contributor/s of the blog who are those that can make the posts.

The blogs initially were used as online diaries and as sites where the creators could have links to other sites that they thought to be interesting and believed that other people would found them useful. But this has changed now the blogs are mainly being used for other reasons such as regular opinion columns, micro-journalism, broadcasting live events etc.

Finally something that is very important with the blogs is that usually are being written from one person or a small team, and this, most of the times, has as result to have a more personal writing style.

So this is my blog, as the most of you can realize it's just a simple blog with only a small number of posts (until now). It is also my first blog which makes me I could say an inexperienced blogger. Before starting writing to my blog the only experience that I had was from other blogs that used and still use to visit often. To be honest it was this module that motivated me to create my own blog and start writing. In contrast with most blogs in my blog you don't find posts only for one topic, I write about anything that find interesting (music, sports, food etc) and sometimes I even write just to express myself.

The implementation of this blog wasn't something difficult and most important wasn't time consuming. I just used one of the most known blog storage services, the Blogger which belongs to Google, and by following some simple steps I had my own blog faster that would ever imagine. With the Blogger except from the general design of the blog with some ready themes that provides you, you can also do a lot more. The Blogger has a lot of differnet gadgets that you can use to make the blog more interesting and useful. Gadgets like the configure link list that I have put on the top right corner where you can add links to sites or other blogs that you find interesting. Also another very useful gadget that can be added and which I have also added is the one that have to do with labels and is exactly under the configure link list. This gadget help us to categorize the posts that we make, for example in my blog I have until now 4 different categories of posts (coursework, sports, food, general). So with this is much easier for every visitor of the blog to find the posts that he/she is more interested in. Moreover there is the blog archive through which everyone can see how often there are new posts. But except from these gadgets, there are also thousands more and every day there are new ones that are being created that can be used to make every blog even more practical.

In addition to all these gadgets I am also using photos and videos in the posts that I make and I have given the ability to every visitor of the blog to comment if he/she wants the posts in order to hear also their opinions on what I am writing. Those two last things I think that are also very important in order to make a blog even more attractive and pleasant to its visitors.

Finally as we mentioned every blog is usually being written from just one person or a small group, in my blog I have added and another contributor who can also make posts but he can not change the outlay of the blog. The only one that can change the outlay of the blog is the creator of the blog, in our case, me.

So this is my blog, one in the millions that exists nowadays.

It's a simple blog but at the same moment it's a blog with its "personality", my personality.

REFERENCES

1. Andy MacFarlane, Susan Jones, Richard Butterworth and Jason Dykes (2009), "Digital Information Technologies and Architectures", Lecture 1: Blogs, City University.
2. http://en.wikipedia.org/wiki/Blog
3. https://www.blogger.com/start
4. http://www.dailyblogtips.com/what-is-a-blog/
5. http://washingtonsquarepark.wordpress.com/2009/01/12/

Το Ταξίδι Ξεκίνησε

Καλημέρα...

Σάββατο σήμερα η επόμενη μέρα της μεγάλης κλήρωσης στο Cape Town της Νότιας Αφρικής. Εκεί χτες το απόγευμα έγινε η κλήρωση για το Μουντιάλ του 2010. Μετά από 16 χρόνια και για δεύτερη φορά στην ιστορία του Ελληνικού ποδοσφαίρου η Εθνική μας ομάδα θα είναι παρούσα.

Και πώς τα έφερε η τύχη και η κληρωτίδα και θα συναντήσουμε τους 2 από τους 3 αντιπάλους που είχαμε και στη πρώτη μας παρουσία το 1994 στα γήπεδα των ΗΠΑ, την Αργεντινή, που τότε είχε παίκτη το μεγάλο Μαραντόνα και αυτή τη φορά θα τον έχει προπονητή, και τη Νιγηρία. Εύχομαι να μην έχουμε παρόμοιο απολογισμό, απέναντι σε αυτές τις 2 ομάδες, όπως και το 1994 όπου, οι περισσότεροι θα το θυμούνται, γνωρίσαμε ήττες με 4-0 από την Αργεντινή και 2-0 από τη Νιγηρία (ούτε στο 3ο ματς τότε απέναντι στη Βουλγαρία είχαμε καταφέρει να σκοράρει). Η τέταρτη ομάδα που συμπληρώνει το καρέ του ομίλους μας είναι η Νότια Κορέα μία ομάδα που μπορεί να μην έχει την ιστορία της Αργεντινής ή ακόμη και της Νιγηρίας αλλά στην οποία θα πρέπει να δώσουμε ιδιαίτερη προσοχή μην ξεχνάμε άλλωστε πως στο Μουντιάλ του 2002 ήταν εκείνη η ομάδα που κατέλαβε την 4η θέση (όπως και αν έγινε αυτό).

Η εθνική μας έχει δείξει ότι είναι δυνατή για το καλύτερο, ειδικά όταν την έχουν ξεγραμμένη... Ας ελπίσουμε ότι στα γήπεδα της Νοτίου Αφρικής και με την υποστήριξη των χιλιάδων Ελλήνων που κατοικούν εκεί αλλά και που θα καταφτάσουν από όλα τα μήκη και πλάτη του πλανήτη θα κάνει αυτό που ξέρει καλά...

Και όπως είπε και γνωστός αθλητικός δημοσιογράφος: "Πάμε για ένα γκολ, μία νίκη και όπου μας βγάλει..." γιάτι και μόνο το γεγονός ότι θα είμαστε εκεί είναι κάτι το μοναδικό...

Καλός Δεκέμβρης...

Καλημέρα σας και καλό μήνα (αν και λίγο καθυστερημένα...),

Πότε πέρασαν οι προηγούμενοι 11 μήνες και μπήκε ο Δεκέμβρης ούτε που το κατάλαβα. Πλησιάζουν τα Χριστούγεννα και ήδη όλους έχει αρχίζει να μας επηρρεάζει το "πνεύμα" των γιορτών "άντε να περάσουν και οι τελευταίες μέρες...άντε να πάρουμε και το 13ο μισθό να πάμε να τον ξεκοκαλίσουμε...άντε να γυρίσουμε σπίτια μας (φοιτητές (συμπεριλαμβανομένου και εμένα) ξενητεμένοι)"!

Εχτές είχαμε και τη γιορτή των Αγγέλων στη Θεσ/νίκη με Χατζηγιάννη υποθέτω ότι για άλλη μία φορά έγινε ένας ψιλοχαμός στο κέντρο της πόλης κόπηκε η κυκλοφορία και τα συνηθισμένα, δεν έχω προλάβει ακόμη να ενημερωθώ αλλά είμαι σίγουρος ότι κάτι τέτοιο θα συνέβει.

Αλλά πέρα από το ότι μπήκε ο Δεκέμβρης ήδη έχουν στολιστεί τα μαγαζιά οι δρόμοι και σιγά σιγά και τα σπίτια, τίποτα άλλο δεν συνηγορεί ότι πλησιάζουμε στα μέσα του χειμώνα ειδικά στην Ελλάδα απ' ότι μαθαίνω ο καιρός είναι ανοιξιάτικος ήλιος και θερμοκρασίες που μερικές φορές ξεπερνάνε και τους 20 βαθμούς. Αλλά και εδώ στο Λονδίνο τα πράγματα δεν πάνε πίσω τις τελευταίες 2 μέρες ο ήλιος έχει την τμητική του αλλά και πιο πριν ο καιρός ήταν αρκετά καλός για τα δεδομένα της Αγγλίας, μόνο λίγο η θερμοκρασία είναι χαμηλή αλλά και πάλι κάτω από τους 4 βαθμούς δεν έχει πέσει, περίεργα πράγματα πολύ περίεργα.
Βέβαια πότε δεν ξέρουμε μπορεί μέχρι τις γιορτές να έχει ανατραπεί τελείως το σκηνικό, και να σας πω τη γνώμη μου μακάρι, φαντάζεστε Χριστούγεννα με 15-20 βαθμούς; Ωραίος ο ήλιος δεν μπορώ να πω αλλά άμα δεν κάνει λίγο κρύο να φορέσεις το κασκόλ σου το σκουφάκι σου τα γαντάκια σου δεν θα ευχαρηστηθείς τις γιορτές. Και θέλω να ελπίζω ότι όλοι συμφωνείτε με αυτό.

Ας ελπίσουμε ότι θα στρώσουν τα πράγματα....

Καλό σας μήνα και πάλι...

Αρχίζει το ματς!

Καλημέρα σας...

Κυριακή σήμερα 29 Νοεμβρίου, μία Κυριακή όμως που ένα μόνο τραγούδι της ταιριάζει...



Και πώς να μην της ταιριάζει όταν έχεις ντέρμπι Ολυμπιακού-Παναθηναϊκού σε μπάσκετ και ποδόσφαιρο στην Ισπανία έχουμε το el classico Μπαρτσελόνα-Ρεάλ Μαδρίτης στο Λονδίνο Άρσεναλ-Τσέλσι, στο Merseyside έχουμε τη μεγάλη ομάδα της Αγγλίας να φιλοξενείται από την Έβερτον και τέλος έχουμε και το μεγάλο ντέρμπι Ντόρας και Αντώνη... :Ρ :Ρ :Ρ!!!!

Εμένα πάντως θα με συγχωρήσετε γιάτι πάνω απ' όλα αυτά θα βάλλω την μεγάλη μου αγάπη τον Άρη, οπότε Άρης-Πανιώνιος στις 16:45 ώρα Ελλάδος ή στις 14:45 ώρα Αγγλίας, πιστεύω ότι ήρθε ο καιρός να επιστρέψουμε στις νίκες, και μετά έπονται όλα τα υπόλοιπα. Το καλό είναι ότι σχεδόν όλα τα άλλα παιχνίδια ξεκινούν αργότερα έτσι θα μπορέσω να παρακολουθήσω τα περισσότερα.

Συνεπώς καταλαβαίνετε ότι είναι μία γεμάτη Αθλητική και Πολιτική Κυριακή για την οποία όμως έχω την κατάλληλη συνταγή...


ΣΥΝΤΑΓΗ ΓΙΑ ΑΘΛΗΤΙΚΗ ΚΑΙ ΠΟΛΙΤΙΚΗ ΚΥΡΙΑΚΗ

2 Κάσες μπύρες/άτομο
1 Ψυγείο, κατά προτίμηση άδειο για να χωρέσει τις μπύρες
Διαφημιστικά από Πιτσαρίες
1 τηλέφωνο για να μπορείτε να παραγγέλνετε

Και το καλύτερο με αυτή τη συνταγή είναι ότι δεν χρειάζεται καν εκτέλεση...!!!!

Οπότε καλή σας όρεξη και καλή σας διασκέδαση...!!!!

Friday Night

Καλησπέρα σας,

Παρασκευή βράδυ το Λονδίνο κινείται όπως και κάθε μέρα αλλά σήμερα λίγο παραπάνω οι περισσότεροι δεν δουλεύουν αύριο, οι φοιτητές και οι μαθητές δεν έχουν μαθήματα (εκτός από αυτούς που έχουν εργασίες... :Ρ :Ρ :Ρ) οπότε καταλαβαίνετε...! Το βασικό είναι ότι σήμερα βοηθάει και ο καίρος δεν βρέχει, έχει όμως τη ψύχρα του, μη τα θέλουμε και όλα δικά μας!

Σήμερα δεν έχει συνταγή για τον αδερφό, αν και μεταξύ μας έκανα κάτι γαρίδες σαγανάκι άλλο πράγμα, αλλά όπως σας είπα θα γράφω ότι θέλω ΓΙΑΤΙ ΕΤΣΙ ΜΟΥ ΑΡΕΣΕΙ...!!

Η δική μου μέρα ήταν ψιλοκουραστική τρεξίματα από εδώ τρεξίματα από εκεί καταλαβαίνετε είμαι πολυάσχολος τύπος, μετά γύρνα σπίτι να μαγειρέψεις οπότε λέω να καθήσω μέσα κρασάκι μία καλή ταινία στο dvd και χαλάρωμα να μην μας βρει το Σαββατοκύριακο "κομμάτια"...!

Αυτά και τίποτα άλλο για την ώρα...
Άντε καλό Σαββατοκύριακο αν και πιστεύω ότι θα τα πούμε και κατα τη διάρκεια του...!

Υ.Γ. Και ένα τραγουδάκι...