OpenLLM-France/wikimedia huggingface dataset:
# A-level Computing/AQA/Paper 2/Fundamentals of databases/Big Data
## Specification

* Specification coverage
* 3.11 Big data

## Big data

Big data is a generic term given to datasets that are so large or complicated that they are difficult to store, manipulate and analyse. The three main features of big data are:
* volume: the sheer amount of data is on a very large scale
* variety: the type of data being collected is wide-ranging, varied and may be difficult to classify.
* velocity: the data changes quickly and may include constantly changing data sources.
The lack of structure in Big Data is considered to be the aspect creating the most difficulties. For this reason, traditional data analysis and organisation methods such as relational databases or SQL are no longer useful when it comes to Big Data . However, when the correct techniques are applied to Big Data, a vast amount of useful information can be revealed. Processing Big Data allows professionals such data scientists to spot and analyse hidden patterns and relationships which wouldn't have been easy to interpret before.
Big data is used for different purposes. In some cases, it is used to record factual data such as banking transactions. However, it is increasingly being used to analyse trends and try to make predictions based on relationships and correlations within the data. Big data is being created all the time in many different areas of life. Examples include:
* scientific research
* retail
* banking
* government
* mobile networks
* security
* real-time applications
* the Internet.
Latency is critical here and could be described as the time delay of the amount of time it takes to turn the raw data into meaningful information. With big data there may be a large degree of latency due to the amount of time taken to access and manipulate the sheer number of records.

## Structured and unstructured data

Most databases work on the model that the data will fall into columns and rows, otherwise referred to as fields and records. This makes data easy to organise and store as they can be entered into the appropriate fields. When data are analysed, it is relatively easy to carry out searches and sorts to query the data. Some data doesn't fit into this model. Data can be defined as either structured or unstructured.
* Structured data: data that can be defined using traditional database techniques using fields and records.
* Unstructured data: data that cannot be defined in columns and rows. These might include multimedia data, web pages and the contents of emails, documents, presentations. This type of data is much harder to analyse.
# A-level Computing/AQA/Paper 2/Fundamentals of databases

* Conceptual data models and entity relationship modelling
* Relational databases
* Database design and normalisation techniques
* Structured Query Language (SQL)
** SELECT
** UPDATE
** INSERT
** DELETE
** Data definition language
* Client server databases
* Big Data
# A-level Computing/AQA/Paper 2/Fundamentals of databases/DELETE

Sometimes you might fall out with friends on Facebook so that you don't even want them to see your restricted page. You'd want to delete your relationship (it's actually likely that Facebook retains the connection but flags it as 'deleted', that isn't important here). The police might also find that a crook is in fact innocent and then want to delete their criminal record. We need a DELETE command to do all of these things, to permanently delete records from databases. Imagine that we find out that Geoff was framed and he is completely innocent:
* Exercise: DELETE statements
* The police have agreed an amnesty with all heavily scarred (4+) women and have decided to delete them from the database. Write a statement to do this.
* Answer:
* DELETE FROM crooks
* WHERE numScars >= 4 AND gender = 'female'
* The police want to delete all minors (people under 16) from their records. Do it!
* Answer:
* DELETE FROM crooks
* WHERE DoB >= 1999
You can use wildcards within a selection statement. For example, to delete all records: DELETE * FROM Customer. You should use such wildcards carefullyǃ
# A-level Computing/AQA/Paper 2/Fundamentals of databases/Data definition language

Data Definition Language (DDL) is a way to adjust the structure of a database. You might have created databases in the past using a GUI such as Access or even MySQL. DDL allows you to create databases from pure code including the ability to:
* Create tables: CREATE TABLE
* Change the structure of a table: ALTER
* Delete tables: DROP
To create a table the user needs to define the name of the table and each of the attributes including the data type and length.
CREATE TABLE Customer(CustomerID varchar(5), CustomerName varchar(255), CustomerAddress varchar(255), PRIMARY KEY (CustomerID));
Examples of supported data types (depending on the database):
| Data type | Description |
| Character (n) | character string with fixed length (n) |
| Varchar (n) | character string variable length with maximum field length (n) |
| Boolean | True or False |
| Int | short for integer and is a whole number |
| Decimal (p,s) | decimal number with number of digits before and after the decimal point |
| Real | any number up to 7 decimal places |
| Date | in the format day, month, year |
| Time | in the format hour, minutes, seconds |

## CREATE

You need to know what they all do (as listed above), though you only need to know how to use the CREATE TABLE command. Let's look at how we could have made the crooks table above:
* Questions
* Write a DDL statement to create the table Customer(CustomerID, CustomerName, Address, Postcode, Email)
* Answer:
* CREATE TABLE customer (
* CustomerID INTEGER PRIMARY KEY,
* CustomerName VARCHAR(16),
* Address VARCHAR(30),
* Postcode VARCHAR(8),
* Email VARCHAR(20)

## ALTER

An ALTER statement in SQL changes the properties of a table in a relational database without the need to access the table manually.

## DROP

Dropping a table is like dropping a nuclear bomb. It is irreversible and generally not recommendedǃ.
By running this line of code, the table "crooks" will be removed from the database with no chance of it being recovered unless backups have been previously made.

## Setting Primary Keys

Primary keys can be set after table creation via the alter statement.
Primary keys can also be set during table creation

## Setting Composite Keys

To set a primary key made up of two columns during table creation you could do something such as this
Where the constraint name would be UserId and the table's primary key would be made up of the user_id and the username columns.
This could also be done after table creation:
# A-level Chemistry/OCR (Salters)/Amount of substance

Amount of substance is a physical quantity. Its symbol is n and its SI unit is the mole, whose symbol is mol.
One mole of objects is 6.0221415 × 10$^{23}$ objects. That's 60 221 415 000 000 000 000 000, or about sixty billion trillion objects. The number 6.0221415 × 10$^{23}$ is called Avogadro's number or Avogadro's constant and has the symbol L. This number is usually rounded down to 6.02 × 10$^{23}$ or 6 × 10$^{23}$.
One mole of a molecular substance is 6 × 10$^{23}$ molecules. One mole of a non-molecular substance (such as NaCl) is 6 × 10$^{23}$ formula units, e.g. 6 × 10$^{23}$ lots of NaCl, so 6 × 10$^{23}$ sodium ions and 6 × 10$^{23}$ chloride ions.
# A-level Chemistry/OCR (Salters)/Atomic orbitals

The electrons in an atom do not follow a fixed orbit like planets orbiting the sun. Electrons are subject to the laws of quantum mechanics, which means their motion is very different to normal, life-sized objects. We describe their location within atoms in terms of three-dimensional "clouds" called orbitals. An orbital can contain a maximum of two electrons, spins paired.
It is important to note that electrons are not entirely confined within the atom. The orbitals shown below give the shapes of the regions that contain the electron 95% of the time. However, the other 5% of the time, the electron is somewhere outside this region. An electron from an atom in your hand may temporarily be on the other side of the moon, but it is only very rarely there, so rarely in fact that we can ignore it for the purposes of understanding the behaviour of atoms.

## p orbitals

There are three p orbitals in a p subshell. They are labelled p$_x$, p$_y$, and p$_z$. The p$_x$ orbital points along the x-axis, the p$_y$ points along the y-axis and the p$_z$ points along the z-axis. This means that the three p orbitals are all at 90° to each other (perpendicular and orthogonal are two words you may see used to mean the same thing).

## d orbitals

The d orbitals have slightly confusing names. From left to right, they are: d$_{z²}$, d$_{x²−y²}$, d$_{xy}$, d$_{xz}$, and d$_{yz}$.
Sometimes, particularly when discussing d orbital splitting in complexes, d orbitals are arranged into two groups based on their symmetry. The d$_{z²}$ and d$_{x²−y²}$ orbitals form a group called e$_g$, while the d$_{xy}$, d$_{xz}$ and d$_{yz}$ orbitals form a group called t$_{2g}$.
# A-level Chemistry/OCR (Salters)/Colour by Design

Colour by Design is the eleventh unit in the Salters Advanced Chemistry course.

## Chemical Storylines sections

* CD1 Ways of making colour
* CD2 The Monastral Blue story
* CD3 Chrome Yellow
* CD4 Chemistry in the art gallery
* CD5 At the start of the rainbow
* CD6 Chemists design colours
* CD7 Colour for cotton
* CD8 High-tech colour
* CD9 Summary

## Chemical Ideas sections

* 6.7 Where does colour come from? (revision)
* 5.1 Ions in solids and solutions (revision)
* 6.8 Ultraviolet and visible spectroscopy
* 13.6 Oils and fats
* 7.3 Chromatography
* 6.1 Light and electrons (revision)
* 12.3 Arenes
* 12.4 Reactions of arenes
* 13.10 Azo compounds
* 6.9 Chemistry of colour

## Activities

* CD1 Changing colours chemically
* CD3 Seeing colours
* CD4.1 Using reflectance spectra to identify pigments
* CD4.2 What factors affect the drying potential of an oil?
* CD4.3 Investigating paint media
* CD4.4 Identifying a pigment
* CD4.5 Finding a perfect match
* CD5 Comparing hydrocarbons
* CD6 Making azo dyes
* CD7.1 Dyeing with a direct dye and a reactive dye
* CD7.2 Different dyes for different fibres
* CD9 Check your notes on Colour by Design

## External links

* CD unit map
* CD Check Your Notes
# A-level Chemistry/OCR (Salters)/Born-Haber cycles
## Atomisation

Atomisation is the process of converting an element in its standard state to a monatomic gas.
The amount of energy required to achieve atomisation is termed the enthalpy change of atomisation, ΔH$_{at}$, measured in kJ mol$^{−1}$.
The quantity you find in most data tables is the standard enthalpy change of atomisation, which is the amount of energy required to convert one mole of an element in its standard state to a monatomic gas, under standard conditions.
The equation for atomisation is:
    ${\frac {1}{n}}{\mbox{E}}_{n}(\sigma )\rightarrow {\mbox{E(g)}}$
    where σ represents the standard state of the element, so
* if E is a solid is its standard state, σ = s
* if E is a liquid is its standard state, σ = l
* if E is a gas is its standard state, σ = g.
For example, the symbol $\Delta H_{at}^{\circ }({\mbox{Na}})$ represents the standard enthalpy change of atomisation of sodium, ${\mbox{Na(s)}}\rightarrow {\mbox{Na(g)}}$
The case of chlorine is slightly more complicated: $\Delta H_{at}^{\circ }({\mbox{Cl}})$ represents the standard enthalpy change of atomisation of chlorine, ${\frac {1}{2}}{\mbox{Cl}}_{2}{\mbox{(g)}}\rightarrow {\mbox{Cl(g)}}$
# A-level Chemistry/OCR (Salters)/Aspects of Agriculture

Aspects of Agriculture is the tenth unit in the Salters Advanced Chemistry course.

## Chemical Storylines sections

* AA1 What do we want from agriculture?
* AA2 The world at your feet
* AA3 Keeping soil fertile
* AA4 Competition for food
* AA5 Summary

## Chemical Ideas sections

* 10.2 The effect of temperature on rate (revision)
* 10.3 The effect of concentration on rate (revision)
* 5.2 Molecules and networks (revision)
* 5.6 Bonding, structure and properties: a summary
* 9.1 Oxidation and reduction (revision)
* 11.3 The p block: nitrogen and Group 5
* 7.3 Equilibria and partial pressures
* '10.4 What is a catalyst? (revision)
* 10.5 How do catalysts work? (revision)
* 3.5 Geometric isomerism (revision)
* 3.6 Optical isomerism (revision)
* 7.4 Partition equilibrium
* 13.5 Esters (revision)

## Activities

* AA2.1 How does temperature affect the rate of a reaction?
* AA3.1 What is the nitrogen content of soils? (Optional extension)
* AA3.2 The nitrogen balance in UK agriculture
* AA3.3 Revising for end of course exams
* AA4.1 Dilemma over malaria
* AA4.2 Partition equilibrium
* AA4.3 What makes an active pyrethroid?
* AA5 Check your notes on Aspects of Agriculture

## External links

* AA unit map
* AA Check Your Notes
# A-level Chemistry/OCR (Salters)/Benzene

Benzene is an aromatic hydrocarbon or arene.

## Structure

The usual structural representation for benzene is a six carbon ring (represented by a hexagon) which includes three double bonds. Each of the carbons represented by a corner is also bonded to one other atom. In benzene itself, these atoms are hydrogens. The double bonds are separated by single bonds so we recognize the arrangement as involving conjugated double bonds. An alternative symbol uses a circle inside the hexagon to represent the six pi electrons.
Instead of having three short double bonds and three long single bonds (above, left), it has six medium-length bonds (above, right).
A double bond is really two bonds, with two electrons in each bond, so four electrons in total in a double bond. Two electrons from each double bond in benzene (if the double bonds really existed, which they don't) are smeared over all six carbon atoms.
Whenever electrons are not confined to a bond between just two atoms, they are called declocalised electrons.
* the full displayed structural formula of benzene
* Kékulé proposed this structure for benzene
* Benzene rings are commonly represented like this
* Space-filling models like this show all C−C and C−H distances are equal
* This electrostatic potential surface shows greater electron density inside the ring
* The π electrons in benzene occupy molecular orbitals like this one, which are delocalised over the entire molecule
Pic
Physical Properties
Boiling point: 80 °C
Melting point: 6 °C
Relative density (water = 1): 0.88
Solubility in water, g/100 ml at 25 °C: 0.18
Vapour pressure, kPa at 20 °C: 10
Relative vapour density (air = 1): 2.7
Relative density of the vapour/air-mixture at 20 °C (air = 1): 1.2
Flash point: -11 °C c.c.
Auto-ignition temperature: 498 °C
Explosive limits, vol% in air: 1.2-8.0
Octanol/water partition coefficient as log Pow: 2.13
# A-level Chemistry/OCR (Salters)/Chip-pan fires
## How chip-pan fires can explode

* Oil gets so hot that it catches fire all by itself.
* Water is poured into the burning chip pan.
* Water is denser than oil, so it sinks to the bottom of the chip pan (shown in red). As the water touches the bottom, it is heated above its boiling point and instantly vaporizes.
* The water vapour expands radpidly, ejecting the burning molten oil out of the chip pan and into the air where its surface area increases greatly and combustion proceeds much faster.
* Oil is heated strongly
* After some time, it gets hot enough to catch fire
* Pouring a very small amount of water into the fire ejects a plume of burning oil
* With all the oil burned, there is no more fuel to supply the fire
# A-level Chemistry/OCR (Salters)/Buffer solutions
## Calculating the pH of a buffer solution

${\mbox{pH}}=-\log _{10}{\left(K_{a}{\frac {\left[{\mbox{acid}}\right]}{\left[{\mbox{salt}}\right]}}\right)}$

### Derivation

For any equilibrium
$a{\mbox{A}}+b{\mbox{B}}\rightleftharpoons c{\mbox{C}}+d{\mbox{D}}\,\!$
the equilibrium constant, K, is defined as
$K={\frac {[{\mbox{C}}]^{c}[{\mbox{D}}]^{d}}{[{\mbox{A}}]^{a}[{\mbox{B}}]^{b}}}$
Therefore, for the dissociation equilibrium of any acid
${\mbox{HA}}{\mbox{(aq)}}\rightleftharpoons {\mbox{H}}^{+}{\mbox{(aq)}}+{\mbox{A}}^{-}{\mbox{(aq)}}\,\!$
the acid dissociation constant, K$_a$, is defined as
$K_{a}={\frac {[{\mbox{H}}^{+}{\mbox{(aq)}}][{\mbox{A}}^{-}{\mbox{(aq)}}]}{[{\mbox{HA}}{\mbox{(aq)}}]}}$
This equation can be rearranged to make [H$^+$(aq)] the subject:
$[{\mbox{H}}^{+}{\mbox{(aq)}}]=K_{a}{\frac {[{\mbox{HA}}{\mbox{(aq)}}]}{[{\mbox{A}}^{-}{\mbox{(aq)}}]}}$
Two assumptions are required:
1 Every A$^−$ ion comes from the salt
    Although this is not quite true, it is a close enough that the pH value we get from the final equation is very close to that found experimentally. It allows us to assume that
    $\left[{\mbox{HA}}{\mbox{(aq)}}\right]=\left[{\mbox{acid}}\right]$
2 Every HA molecule remains undissociated
    Again, despite being slightly inaccurate, this assumption creates the following useful equation
    $\left[{\mbox{A}}^{-}{\mbox{(aq)}}\right]=\left[{\mbox{salt}}\right]$
The equations in assumptions 1 and 2 allow us to replace [A$^−$(aq)] with [salt] and [HA(aq)] with [acid] as follows.
The effect of assumption 1 is that
$[{\mbox{H}}^{+}{\mbox{(aq)}}]=K_{a}{\frac {[{\mbox{HA}}{\mbox{(aq)}}]}{[{\mbox{A}}^{-}{\mbox{(aq)}}]}}$
becomes
$[{\mbox{H}}^{+}{\mbox{(aq)}}]=K_{a}{\frac {[{\mbox{HA}}{\mbox{(aq)}}]}{[{\mbox{salt}}]}}$
The effect of assumption 2 is that
$[{\mbox{H}}^{+}{\mbox{(aq)}}]=K_{a}{\frac {[{\mbox{HA}}{\mbox{(aq)}}]}{[{\mbox{salt}}]}}$
becomes
$[{\mbox{H}}^{+}{\mbox{(aq)}}]=K_{a}{\frac {[{\mbox{acid}}]}{[{\mbox{salt}}]}}$
By definition,
${\mbox{pH}}=-\log _{10}{\left(\left[{\mbox{H}}^{+}{\mbox{(aq)}}\right]\right)}$
so
${\mbox{pH}}=-\log _{10}{\left(K_{a}{\frac {\left[{\mbox{acid}}\right]}{\left[{\mbox{salt}}\right]}}\right)}$
# A-level Chemistry/OCR (Salters)/Chemical Ideas/Table of contents

| Chapter | Section | Both | Title | First page | Year |
| 1 | 1 | 1.1 | Amount of substance | 1 | AS |
| 1 | 2 | 1.2 | Balanced equations | 7 | AS |
| 13 | 9 | 13.9 | Amino acids | 336 | A2 |
| 13 | 10 | 13.10 | Azo compounds | 338 | A2 |
# A-level Mathematics/Edexcel/Mechanics 1/Mathematical Models in Mechanics

Mathematical modelling is the process of translating a real world problem into the language of mathematics, allowing the problem to be solved and a solution produced. The more accurate the model can result in a more accurate solution.

## Terminology

This terminology is used in modelling:

### Particle

A body whose dimensions are so small compared with other lengths involved, it can be represented as a single point.

### Bead

A particle with a hole through the centre, allowing it to be threaded onto a string.

### Lamina

A flat object whose thickness is small, compared with its length and breadth. In a uniform lamina equal areas have equal masses.

### Rigid body

An object made of particles which stay in the same position, relative to each other, regardless of the forces acting on it.

### Rod

An object that only has length, and all its mass acts along a line. In a uniform rod equal lengths have equal masses. In a non-uniform rod, equal lengths do not have equal masses.

### Light object

An object that is assumed to have no mass.

### Inextensible String

A string that has a constant length regardless of the forces acting on it.

### Smooth surface

A surface that has no frictional forces.

### Peg

A support from which a body may hang or rest.
# A-level Mathematics/Edexcel/Mechanics 2/Particle Kinematics
## Kinematics of a particle moving in a straight line or plane
### Projectiles

Projectiles are objects, like cannonballs, that move freely under gravity along a curved. When dealing with projectiles in M2 we make a number of assumptions:
* There is no force acting horizontally on the particle (such as air-resistance).
* The only force acting vertically on the particle is gravity.
The key to understanding projectiles is to consider the particle in two dimensions, let's call them x and y. The in the x direction, the particles motion is unchanged (because there is no air resistance) and in the y direction, the particle is accelerating due to gravity. For example, a penny which is thrown horizontally from the top of a building will continue to move away from the building as it falls (horizontal motion does not stop as the velocity of the coin increases, it just becomes less noticeable).
The hardest part of most questions involving projectiles is resolving the particle's velocity into the x and y plane. For any angle at which a particle is projected the horizontal component is given by $V\cos {\theta }$ and the vertical is given by $V\sin {\theta }$. This makes sense, as if you have a particle projected at 90° to the horizontal, then the vertical component is given by $V\sin {90}$ (which is simply V) and the horizontal component by $V\cos {\theta }$ - or 0. Similarly if our particle is projected at 0°, then our horizontal is V and our vertical is 0.
Once the particle is in motion, you can solve equations separately on the x and y directions. So for example you could use the equation $v=u+at$ to work out how fast the particle is travelling vertically after it hits a wall 5 metres away.
# A-level Mathematics/Edexcel/Statistics 2

Statistics 2 (S2), is the second statistics module, and builds on the knowledge already acquired from the previous modules (C1 and S1). The examination consists of one 1½ hour paper.
Note: This book is so you can gain an alternative explanation for the concepts described and it should NOT replace your S2 book.

## Module content

* The binomial and Poisson distributions
* Continuous random variables
* Continuous distributions
* Hypothesis tests
# A-level Mathematics/Edexcel/Mechanics 1/Statics of a particle

$$A car of total mass 1200 kg is moving along a straight horizontal road at a speed of 40 m/s,when the brakes are fully applied ,they exert a constant force and the car comes to rest after travelling a distance of 80m.The resistance to motion from all factors other than the brakes is assumed to be constant and of magnitude 500N.Find the magnitude of the force exerted by the brakes when fully applied.
# A-level Mathematics/Edexcel/Mechanics 2

Mechanics 2 is an applied maths module for the edexcel exam board for A-Levels.
Note: This book is so you can gain an alternative explanation for the concepts described and it should NOT replace your M2 book.
It comprises the following modules:
* Particle Kinematics
* Centres of Mass
* Work, Energy & Power
* Collisions
* Statics of Rigid Bodies
# A-level Mathematics/Edexcel/Mechanics 3

Mechanics 3 is an applied maths module for the Edexcel exam board for A-Levels.
It comprises the following modules:
* Further Kinematics
* Elastic Strings and Springs
* Further Dynamics
* Motion in a Circle
* Statics of Rigid Bodies
# A-level Mathematics/Edexcel/Statistics 3

Statistics 3 (S3), is the third statistics module, and builds on the knowledge already acquired from earlier statistics modules.
Topics within Statistics 3 include:
-Chapter 1: Combinations of random variables
-Chapter 2: Sampling
-Chapter 3: Estimation, confidence intervals and tests
-Chapter 4: Goodness of fit and contingency tables
-Chapter 5: Regression and correlation
Students looking for additional past papers may find use from the International A Level Papers, and the Solomon Press A Level Papers.
Note: This book is so you can gain an alternative explanation for the concepts described and it should NOT replace your S3 book.
# A-level Mathematics/Edexcel/Statistics 2/The binomial and Poisson distributions
## Factorial notation

A factorial of a positive integer n is the product of all the natural numbers from 1 to n. The factorial of n is denoted by n! (n factorial). Factorials are used in probability distributions.
Factorials can be used to find the possible number of permutations or combinations of the elements of a set. For example, let S represent the set of beads in a bag. The bag has 2 blue and 2 green beads. The beads are taken out of the bag and arranged. The possible arrangements are:
* BBGG
* BGGB
* BGBG
* GBGB
* GBBG
* GGBB
where B represents a blue bead and G represents a green bead.
We can see that there are 8 possible arrangements. We can use factorials to work out the number of possible arrangements.