Samenvatting

Summary Everything you need for the IDT exam!

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Tilburg University (UVT)

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Samenvatting IDT

Week 1.
We are currently see increasing growth of the data. This is big data.

What are the reasons for DBMS (data-base management-systems)?

In the early days: database applications were built on top of file systems. This means that you had a
computer on which you included all info in files, and then you had to somehow retrieve information from
these files. This has many drawbacks:

1. You had data redundancy and inconsistency:
a. different information (inconsistency). Redundancy = the same information in different
files, because you need to do that.
b. For example data from university: you have one file of the student, and another file of the
registration for courses of the student, so if one student would change information and
you only modified one of the files, the other file would be in an inconsistent state
2. Difficulty in accessing data: need to write a new program to carry out each new task.
3. Data isolation: one file could follow one format, and another file could follow another format (e.g.,
how you write dd/yy/mm).
4. Integrity problems:
a. Integrity constraints (e.g., account balance > 0) become “buried” in program code rather
than being stated explicitly
b. Hard to add new constraints or change existing ones
5. Atomicity of updates
a. Example: Transfer of funds from one account to another should either complete or not
happen at all
b. Failures may leave data in an inconsistent state with partial updates carried out
6. Concurrent access by multiple users.
a. Necessary for performance
b. Uncontrolled concurrent (two users at the same time) access can lead to inconsistenecies
c. Example: Both people were reading the balance of a banking system, and withdrawing at
the same time, you should be careful. First one read 100 and wanted to withdraw 50, and
the other wanted to withdraw 70. If one of them wouldn’t lock the file, the one of them
would overwrite the info of the other. This can lead to inconsistencies.
7. Security problems; we want to keep different levels of access to different users. Which is hard
when using different files. Either access is given or not.

DBMS offers solutions to all!

,DBMS architecture:
• Database (DB):
o Collection of data with the same structure for all data
o Including correlations and relationships
o Common purpose, i.e., The data that is in the DB, is there for a purpose → the purpose is what
the company is doing. So it is expected from this data that it has correlations and relations
o Shared/used by multiple users
• Database Management System (DBMS):
o Collection of programs over DB. It offers functionalities/methods to:
▪ Define, i.e., specify the data types, structure, constraints
▪ Build & manipulate, i.e., store on disk, retrieve, update
▪ Administrate, e.g., manage access rights
• Applications:
o Access to DB for performing queries
o Android app, Web application, etc.
▪ Currently we have different devices, a laptop, phone, etc. to access the same
information you have different layouts. The information is the same. So you can
have different interfaces.
▪ Basically, you can see the DBMS as a black box interacting between
users/applications and the actual database.

Different DBMS examples:
• Airlines: reservation and schedule information. Among the first to use databases in a
geographically distributed manner.
• Banking: customer information, accounts, loans, and transactions.
• University: student information, course registration, grades. Application program examples:
• Add new students, lectures, courses.
• Register students, lectures, courses.
• Assign grades, generate transcripts.

The ultimate goal of DBMS is to separate the data from the application.

• DBMS provide an interface that the application programmer must follow.
• Allow system administrator to make modifications without having an impact on the user.
o E.g. improve or reconfigure. The actual end user doesn’t need to see the
information in the inside.
• The users can change their view of the data without having to worry about how the data
is stored.

➔ In order for this to happen, the DBMS is composed by 3 layers.

,3 layers of a DMBS

1. External layer: communication of users → dialog
• Analysis of user requests (queries).
• Access control (not all users can access all).
• Answer presentation.
2. Logical layer → control
• Optimization of queries.
• Resolving conflicting access, i.e. multiple users.
• Guarantees constant availability even in case of failures.
o E.g., store the data in multiple databases → failure resilient
3. Internal layer → storage
• Storing the data.
• Software for structuring the data.
• Efficient access methods → keys, indices, etc.

Development process (lifecycle)
1. Planning:
Develop a preliminary understanding of the business situation and how information systems might
help solve the problem. This step includes:
a. Analyzing current data processing.
b. Analyzing general business functions and needs.

2. Analysis:
a. Analyze the business situation. Thoroughly to determine requirements and to structure
those requirements.
b. Output of this analysis: conceptual schema.
i. This corresponds to a detailed, technology independent specification of the
overall organizational data structure → it is a description of what the company
would like to develop, and it is not bounded to a particular technology → to
generate a conceptual schema we use an entity relation model:
c. An example of this analysis is the entity relationship model

, 3. Design: there are two different designs, logical and physical:
• Logical design: representation of the database.
o You transform the conceptual schema (output of
previous step) in something that the DBMS can use.
• Physical: the set of specifications that describe how data are
stored in a computer’s secondary memory by a specific
database management system.
o Keep in mind that you have different systems. How
the data is stored, doesn’t have to be the same.

4. Implementation: once you have built the database, you include the
data (populate it)
a. Install the applications and do some testing.
b. Complete documentation and generate training materials.

5. Maintenance:
• Monitor: the operation and usefulness of the system.
• Repair: by fixing errors in database and applications.
• Enhance: by analyzing the database and applications to ensure that evolving information
requirements are met.

You can have different types of DBMS:
• Traditional → use text and numerical data.
• Multimedia → multimedia data (movies, music, etc.).
• Spatial → geographic and geometric data.
• Data warehouses.

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