diff --git a/Week4/homework/ex1-aggregation/index.js b/Week4/homework/ex1-aggregation/index.js
new file mode 100644
index 000000000..5adf824d3
--- /dev/null
+++ b/Week4/homework/ex1-aggregation/index.js
@@ -0,0 +1,100 @@
+import { MongoClient } from "mongodb";
+import "dotenv/config";
+const clientMongo = new MongoClient(process.env.MONGODB_URL);
+import fs from "fs";
+import csv from "csv-parser";
+let data;
+
+async function processCSV(fileName) {
+  return new Promise((resolve, reject) => {
+    const data = [];
+    fs.createReadStream(fileName)
+      .pipe(csv())
+      .on("data", (row) => data.push(row))
+      .on("end", () => resolve(data))
+      .on("error", (err) => reject(err));
+  });
+}
+
+async function getTotalPopulationByYear(collection, country) {
+  const result = await collection
+    .aggregate([
+      { $match: { Country: country } },
+      {
+        $group: {
+          _id: { $toInt: "$Year" },
+          countPopulation: {
+            $sum: {
+              $add: [{ $toInt: "$M" }, { $toInt: "$F" }],
+            },
+          },
+        },
+      },
+      { $sort: { _id: 1 } },
+    ])
+    .toArray();
+  return result;
+}
+
+async function getContinentsPopulation(collection, year, age) {
+  const result = await collection
+    .aggregate([
+      {
+        $match: {
+          Year: year.toString(),
+          Age: age.toString(),
+          // Filter only continents by checking if Country is uppercase
+          $expr: {
+            $eq: ["$Country", { $toUpper: "$Country" }],
+          },
+        },
+      },
+      {
+        $addFields: {
+          TotalPopulation: { $add: [{ $toInt: "$M" }, { $toInt: "$F" }] },
+        },
+      },
+      {
+        $project: {
+          _id: 1,
+          Country: 1,
+          Year: 1,
+          Age: 1,
+          M: 1,
+          F: 1,
+          TotalPopulation: 1,
+        },
+      },
+    ])
+    .toArray();
+  return result;
+}
+
+async function main() {
+  try {
+    await clientMongo.connect();
+    const db = clientMongo.db("databaseWeek4");
+    const collection = db.collection("population_pyramid");
+    data = await processCSV(
+      "./Week4/homework/ex1-aggregation/population_pyramid_1950-2022.csv"
+    );
+    await collection.insertMany(data);
+    data = await getTotalPopulationByYear(collection, "Netherlands");
+    console.log(
+      "\nPopulation by Year (Netherlands):\n",
+      JSON.stringify(data, null, 2)
+    );
+    data = await getContinentsPopulation(collection, "2020", "100+");
+    console.log(
+      "\nPopulation by Continent (2020, 100+):\n",
+      JSON.stringify(data, null, 2)
+    );
+  } catch (error) {
+    console.error("Error connecting to MongoDB:", error);
+  } finally {
+    await clientMongo.close();
+    console.log("Connection to MongoDB closed");
+  }
+}
+
+main();
diff --git a/Week4/homework/ex2-transactions/data.json b/Week4/homework/ex2-transactions/data.json
new file mode 100644
index 000000000..7c813b96d
--- /dev/null
+++ b/Week4/homework/ex2-transactions/data.json
@@ -0,0 +1,41 @@
+{
+  "accounts": [
+    { "account_number": 101, "balance": 5000 },
+    { "account_number": 102, "balance": 12000 },
+    { "account_number": 103, "balance": 7500 },
+    { "account_number": 104, "balance": 3000 },
+    { "account_number": 105, "balance": 9500 }
+  ],
+  "account_changes": [
+    {
+      "account_number": 101,
+      "amount": 1000,
+      "changed_date": "2025-09-01",
+      "remark": "Salary deposit"
+    },
+    {
+      "account_number": 102,
+      "amount": -500,
+      "changed_date": "2025-09-02",
+      "remark": "Grocery shopping"
+    },
+    {
+      "account_number": 103,
+      "amount": 2000,
+      "changed_date": "2025-09-03",
+      "remark": "Freelance payment"
+    },
+    {
+      "account_number": 104,
+      "amount": -1000,
+      "changed_date": "2025-09-04",
+      "remark": "Rent payment"
+    },
+    {
+      "account_number": 105,
+      "amount": 1500,
+      "changed_date": "2025-09-05",
+      "remark": "Gift received"
+    }
+  ]
+}
diff --git a/Week4/homework/ex2-transactions/index.js b/Week4/homework/ex2-transactions/index.js
new file mode 100644
index 000000000..61b11d0df
--- /dev/null
+++ b/Week4/homework/ex2-transactions/index.js
@@ -0,0 +1,23 @@
+import { setup } from "./setup.js";
+import { transfer } from "./transfer.js";
+let clientMongo, account;
+async function main() {
+  try {
+    ({ clientMongo, account } = await setup());
+    const transactionDetails = {
+      donator_account_number: 101,
+      receiver_account_number: 102,
+      amount: 1000,
+      changed_date: new Date().toISOString().slice(0, 10), // 'YYYY-MM-DD'
+      remark: `Transfer from 101 to 102`,
+    };
+    await transfer(clientMongo, account, transactionDetails);
+  } catch (error) {
+    console.error("Error:", error);
+  } finally {
+    await clientMongo.close();
+    console.log("Connection to MongoDB closed");
+  }
+}
+
+main();
diff --git a/Week4/homework/ex2-transactions/setup.js b/Week4/homework/ex2-transactions/setup.js
new file mode 100644
index 000000000..e35972546
--- /dev/null
+++ b/Week4/homework/ex2-transactions/setup.js
@@ -0,0 +1,24 @@
+import { MongoClient } from "mongodb";
+import "dotenv/config";
+import fs from "fs";
+
+export async function setup() {
+  const { accounts, account_changes } = JSON.parse(
+    fs.readFileSync("./Week4/homework/ex2-transactions/data.json")
+  );
+  const clientMongo = new MongoClient(process.env.MONGODB_URL);
+  await clientMongo.connect();
+  const db = clientMongo.db("databaseWeek4");
+  const account = await db.createCollection("accounts");
+  await account.deleteMany({});
+  for (const acc of accounts) {
+    acc.account_changes = account_changes
+      .filter((a) => a.account_number === acc.account_number)
+      .map((a) => {
+        delete a.account_number;
+        return a;
+      });
+    await account.insertOne(acc);
+  }
+  return { clientMongo, account };
+}
diff --git a/Week4/homework/ex2-transactions/transaction.js b/Week4/homework/ex2-transactions/transaction.js
new file mode 100644
index 000000000..93f4e8f91
--- /dev/null
+++ b/Week4/homework/ex2-transactions/transaction.js
@@ -0,0 +1,48 @@
+import { Client } from "pg";
+const config = {
+  host: "localhost",
+  user: "hyfuser",
+  password: "hyfpassword",
+  database: "transactions_week3",
+  port: 5432,
+};
+const client = new Client(config);
+
+async function seedDatabase(client) {
+  try {
+    await client.connect();
+    console.log("Connected to PostgreSQL database!");
+
+    const donator_account_number = 101;
+    const receiver_account_number = 102;
+    const amount = 1000;
+    const changed_date = new Date().toISOString().slice(0, 10); // 'YYYY-MM-DD'
+    const remark = `Transfer from 101 to 102`;
+
+    await client.query("BEGIN");
+    await client.query(
+      "UPDATE ACCOUNT SET balance = balance - $1 WHERE account_number = $2",
+      [amount, donator_account_number]
+    );
+    await client.query(
+      "UPDATE ACCOUNT SET balance = balance + $1 WHERE account_number = $2",
+      [amount, receiver_account_number]
+    );
+    await client.query(
+      "INSERT INTO account_changes(account_number, amount, changed_date, remark) VALUES($1, $2, $3, $4)",
+      [donator_account_number, -amount, changed_date, remark]
+    );
+    await client.query(
+      "INSERT INTO account_changes(account_number, amount, changed_date, remark) VALUES($1, $2, $3, $4)",
+      [receiver_account_number, amount, changed_date, remark]
+    );
+    await client.query("COMMIT");
+    console.log("Transaction completed!");
+  } catch (error) {
+    console.error("Error seeding database:", error);
+  } finally {
+    await client.end();
+  }
+}
+
+seedDatabase(client);
diff --git a/Week4/homework/ex2-transactions/transfer.js b/Week4/homework/ex2-transactions/transfer.js
new file mode 100644
index 000000000..9c28bd2a7
--- /dev/null
+++ b/Week4/homework/ex2-transactions/transfer.js
@@ -0,0 +1,42 @@
+export async function transfer(clientMongo, account, transactionDetails) {
+  const {
+    donator_account_number,
+    receiver_account_number,
+    amount,
+    changed_date,
+    remark,
+  } = transactionDetails;
+  const session = clientMongo.startSession();
+  const transactionOptions = {
+    readPreference: "primary",
+    readConcern: { level: "local" },
+    writeConcern: { w: "majority" },
+  };
+  try {
+    await session.withTransaction(async () => {
+      await account.updateOne(
+        { account_number: donator_account_number },
+        {
+          $inc: { balance: -amount },
+          $push: { account_changes: { amount: -amount, changed_date, remark } },
+        },
+        { session }
+      );
+      await account.updateOne(
+        { account_number: receiver_account_number },
+        {
+          $inc: { balance: amount },
+          $push: { account_changes: { amount: amount, changed_date, remark } },
+        },
+        { session }
+      );
+    }, transactionOptions);
+    console.log("Transaction committed.");
+  } catch (error) {
+    console.log("Transaction aborted.", error);
+    throw new Error(error);
+  } finally {
+    await session.endSession();
+    console.log("Transaction completed!");
+  }
+}
diff --git a/package-lock.json b/package-lock.json
new file mode 100644
index 000000000..da3a745b9
--- /dev/null
+++ b/package-lock.json
@@ -0,0 +1,185 @@
+{
+  "name": "databases-Cohort53",
+  "lockfileVersion": 3,
+  "requires": true,
+  "packages": {
+    "": {
+      "dependencies": {
+        "csv-parser": "^3.2.0",
+        "dotenv": "^17.2.2",
+        "mongodb": "^6.19.0"
+      }
+    },
+    "node_modules/@mongodb-js/saslprep": {
+      "version": "1.3.0",
+      "resolved": "https://registry.npmjs.org/@mongodb-js/saslprep/-/saslprep-1.3.0.tgz",
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+      "license": "MIT",
+      "dependencies": {
+        "sparse-bitfield": "^3.0.3"
+      }
+    },
+    "node_modules/@types/webidl-conversions": {
+      "version": "7.0.3",
+      "resolved": "https://registry.npmjs.org/@types/webidl-conversions/-/webidl-conversions-7.0.3.tgz",
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+      "license": "MIT"
+    },
+    "node_modules/@types/whatwg-url": {
+      "version": "11.0.5",
+      "resolved": "https://registry.npmjs.org/@types/whatwg-url/-/whatwg-url-11.0.5.tgz",
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+      "license": "MIT",
+      "dependencies": {
+        "@types/webidl-conversions": "*"
+      }
+    },
+    "node_modules/bson": {
+      "version": "6.10.4",
+      "resolved": "https://registry.npmjs.org/bson/-/bson-6.10.4.tgz",
+      "integrity": "sha512-WIsKqkSC0ABoBJuT1LEX+2HEvNmNKKgnTAyd0fL8qzK4SH2i9NXg+t08YtdZp/V9IZ33cxe3iV4yM0qg8lMQng==",
+      "license": "Apache-2.0",
+      "engines": {
+        "node": ">=16.20.1"
+      }
+    },
+    "node_modules/csv-parser": {
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+      "license": "MIT",
+      "bin": {
+        "csv-parser": "bin/csv-parser"
+      },
+      "engines": {
+        "node": ">= 10"
+      }
+    },
+    "node_modules/dotenv": {
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+      "resolved": "https://registry.npmjs.org/dotenv/-/dotenv-17.2.2.tgz",
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+      "engines": {
+        "node": ">=12"
+      },
+      "funding": {
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+    "node_modules/memory-pager": {
+      "version": "1.5.0",
+      "resolved": "https://registry.npmjs.org/memory-pager/-/memory-pager-1.5.0.tgz",
+      "integrity": "sha512-ZS4Bp4r/Zoeq6+NLJpP+0Zzm0pR8whtGPf1XExKLJBAczGMnSi3It14OiNCStjQjM6NU1okjQGSxgEZN8eBYKg==",
+      "license": "MIT"
+    },
+    "node_modules/mongodb": {
+      "version": "6.19.0",
+      "resolved": "https://registry.npmjs.org/mongodb/-/mongodb-6.19.0.tgz",
+      "integrity": "sha512-H3GtYujOJdeKIMLKBT9PwlDhGrQfplABNF1G904w6r5ZXKWyv77aB0X9B+rhmaAwjtllHzaEkvi9mkGVZxs2Bw==",
+      "license": "Apache-2.0",
+      "dependencies": {
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+        "bson": "^6.10.4",
+        "mongodb-connection-string-url": "^3.0.0"
+      },
+      "engines": {
+        "node": ">=16.20.1"
+      },
+      "peerDependencies": {
+        "@aws-sdk/credential-providers": "^3.188.0",
+        "@mongodb-js/zstd": "^1.1.0 || ^2.0.0",
+        "gcp-metadata": "^5.2.0",
+        "kerberos": "^2.0.1",
+        "mongodb-client-encryption": ">=6.0.0 <7",
+        "snappy": "^7.3.2",
+        "socks": "^2.7.1"
+      },
+      "peerDependenciesMeta": {
+        "@aws-sdk/credential-providers": {
+          "optional": true
+        },
+        "@mongodb-js/zstd": {
+          "optional": true
+        },
+        "gcp-metadata": {
+          "optional": true
+        },
+        "kerberos": {
+          "optional": true
+        },
+        "mongodb-client-encryption": {
+          "optional": true
+        },
+        "snappy": {
+          "optional": true
+        },
+        "socks": {
+          "optional": true
+        }
+      }
+    },
+    "node_modules/mongodb-connection-string-url": {
+      "version": "3.0.2",
+      "resolved": "https://registry.npmjs.org/mongodb-connection-string-url/-/mongodb-connection-string-url-3.0.2.tgz",
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+      "license": "Apache-2.0",
+      "dependencies": {
+        "@types/whatwg-url": "^11.0.2",
+        "whatwg-url": "^14.1.0 || ^13.0.0"
+      }
+    },
+    "node_modules/punycode": {
+      "version": "2.3.1",
+      "resolved": "https://registry.npmjs.org/punycode/-/punycode-2.3.1.tgz",
+      "integrity": "sha512-vYt7UD1U9Wg6138shLtLOvdAu+8DsC/ilFtEVHcH+wydcSpNE20AfSOduf6MkRFahL5FY7X1oU7nKVZFtfq8Fg==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=6"
+      }
+    },
+    "node_modules/sparse-bitfield": {
+      "version": "3.0.3",
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+      "license": "MIT",
+      "dependencies": {
+        "memory-pager": "^1.0.2"
+      }
+    },
+    "node_modules/tr46": {
+      "version": "5.1.1",
+      "resolved": "https://registry.npmjs.org/tr46/-/tr46-5.1.1.tgz",
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+      "license": "MIT",
+      "dependencies": {
+        "punycode": "^2.3.1"
+      },
+      "engines": {
+        "node": ">=18"
+      }
+    },
+    "node_modules/webidl-conversions": {
+      "version": "7.0.0",
+      "resolved": "https://registry.npmjs.org/webidl-conversions/-/webidl-conversions-7.0.0.tgz",
+      "integrity": "sha512-VwddBukDzu71offAQR975unBIGqfKZpM+8ZX6ySk8nYhVoo5CYaZyzt3YBvYtRtO+aoGlqxPg/B87NGVZ/fu6g==",
+      "license": "BSD-2-Clause",
+      "engines": {
+        "node": ">=12"
+      }
+    },
+    "node_modules/whatwg-url": {
+      "version": "14.2.0",
+      "resolved": "https://registry.npmjs.org/whatwg-url/-/whatwg-url-14.2.0.tgz",
+      "integrity": "sha512-De72GdQZzNTUBBChsXueQUnPKDkg/5A5zp7pFDuQAj5UFoENpiACU0wlCvzpAGnTkj++ihpKwKyYewn/XNUbKw==",
+      "license": "MIT",
+      "dependencies": {
+        "tr46": "^5.1.0",
+        "webidl-conversions": "^7.0.0"
+      },
+      "engines": {
+        "node": ">=18"
+      }
+    }
+  }
+}
diff --git a/package.json b/package.json
new file mode 100644
index 000000000..5822ae68d
--- /dev/null
+++ b/package.json
@@ -0,0 +1,8 @@
+{
+  "dependencies": {
+    "csv-parser": "^3.2.0",
+    "dotenv": "^17.2.2",
+    "mongodb": "^6.19.0"
+  },
+  "type": "module"
+}