SENG1050 Cheatsheet · Web Technologies · Rules, Syntax & Decisions

0 · Exam Map COURSE DATA · FAQ

Permitted materials · verbatim"What can I bring into the exam hall? Stationery. Non-programmable calculator. 1 A4 memory aid." (SENG1050 Formal Examination FAQs)

Practice-paper shape: 120 min + 10 min reading; A: 10 MCQ/20 marks; B: 6 short answers/50; C: 3 long answers/30. Section C = code writing + Huffman.

1 · Networks & Addressing W1–2

Routing chooses an end-to-end path and builds the table; forwarding uses header + table to move one arriving packet to an output. IP names/routes unreliably; TCP adds connection, ordering and reliability. Ports identify applications: HTTP 80, HTTPS 443.

IPv4 block → 8 bits using 128 64 32 16 8 4 2 1.
CIDR a.b.c.d/x: x leading bits identify network.
HTTP class: 1 info · 2 success · 3 redirect · 4 client · 5 server error.

2 · HTML Structure W2

Minimal valid document<!DOCTYPE html>
<html><head><meta charset="UTF-8">
<title>…</title></head>
<body><h1>…</h1>…</body></html>

Head = metadata, title, encoding. Body = displayed content. An element is start tag + content + end tag; void elements have no content/end tag. Phrasing content cannot contain block content such as p.

3 · XML + DTD Method W3 · STARRED

<!ELEMENT menu (dish+)>
<!ELEMENT dish (name,price?)>
<!ATTLIST dish type CDATA #IMPLIED>
none=exactly 1 · +=1+ · *=0+ · ?=0/1
, = sequence · | = choice

Exam First classify well-formed versus valid; a syntactically correct tree may still violate the DTD.

4 · CSS Rule Selection W4 · STARRED

5 · Forms + Layout W5

Every control needs a name; it becomes the server key. Match label for to control id. Radios in one group share a name and allow one value; checkboxes allow several. Group with fieldset + legend. Form action = receiving program.

Table: caption → thead/tbody → tr → th/td.
colspan reduces cells in that row; rowspan occupies position in later rows.

6 · Client–Server + PHP W6

Apache: document root publishes files; virtual hosts allow multiple sites. ServerSignature Off + ServerTokens Prod reduce leakage. Browser gets PHP output, not source.

$qty=(int)$_GET["qty"];
$price=(float)$_GET["price"];
$total=$qty*$price;
echo "<p>$total</p>";

7 · CMS + XPath W7

CMA = authorised administrative back end that creates/edits content. CDA = public read-only front end that compiles/caches pages. Apply least privilege.

$xml=simplexml_load_file("films.xml");
$nodes=$xml->xpath('//film[@rating]');
foreach($nodes as $film) echo $film->title;

xpath() returns an array; use [0] for first node. XPath counts from 1; PHP arrays from 0. Attribute: $film["rating"].

CSS conflict checkpoint

source priority → specificity IDs | classes+pseudo | elements → exact tie: later rule wins.

One ID outranks any number of classes. External CSS holds rules only. Link reset before your sheet. px = 1/96 inch; em follows parent; rem follows root.

8 · JavaScript + DOM W8

function checkQty(){
var q=document.getElementById("qty").value;
if(q===""){alert("Enter quantity");return false;}
return true;}
<form onsubmit="return checkQty();">

9 · Site Design + SEO W9

Speed: size/compress/lazy-load images; defer blocking JS; load essential CSS first. The lecture warns that pages over about three seconds lose roughly half their traffic. Responsive: flexible layout + media queries.

Structure: linear suits fixed sequences; augmented linear adds a return-to-start link; hierarchy suits categories. Avoid a hierarchy so deep that the three-click rule fails or so broad that menus exceed about four manageable chunks.

SEO: unique title, meta description, natural keywords, alt text, clear links and trusted inbound links. A sitemap helps large or new sites with few external links. Crawlers read markup/text. SEO = organic; paid listings = search marketing.

10 · Encoding + Compression W10 · CERTAIN

original=characters×8
compressed=Σ(frequency×code length)
saving=1−compressed/original

Huffman ties may change codes, not total bits. State tie rule. ASCII = 7 bits; Unicode covers over a million characters; UTF-8 uses 8-bit units. Week 10 marks CRC + Huffman as certain exam content.

11 · Encryption Chooser W11

Goals: authentication, integrity, non-repudiation, confidentiality. TLS/PGP use asymmetric encryption to carry a random session key, then symmetric encryption for data. A certificate contains owner identity and public key, issuer, validity period, serial number and issuer signature.

RSA: primes p,q → n=pq → φ=(p−1)(q−1) → public e coprime with φ → private d: ed≡1 (mod φ).

Substitution preserves frequencies; transposition reorders; XOR flips bits. A counterfeit-key attacker substitutes a directory key; certificate signatures defend the binding. Always name whose key.

12 · Security, Privacy, Ethics W12

Cookies are text files, not executable, but permit tracking. Personally identifiable information identifies, locates or contacts a person. Informed consent follows full relevant disclosure. Ethics asks right/wrong; law is government-made rules—legal need not mean ethical.

Answer Threat → attack stage → targeted layered defence → how it breaks that stage.

13 · Final-Question Triage REVIEW + PRACTICE

Long answer Allocate time by marks. Skeleton first; final pass for tags, braces, semicolons, names, branch labels and ratio direction.

14 · HTTP + Web Stack Recall W1–2 · W6

GET /catalogue/index.html HTTP/1.1
Host: shop.example.com.au
2xx success · 3xx redirect · 4xx client · 5xx server

IPv4 drill: convert each decimal block separately into exactly eight bits. DNS drill: names help people; routers need numeric IP addresses.

15 · Worked 1: CSS Box CH4 WORKED EXAMPLE

Given: width 200px, padding 10px, border 2px, margin 15px.

1. Visible border box = 200 + 2×10 + 2×2 = 224px.
2. Occupied space = 224 + 2×15 = 254px.
3. With box-sizing:border-box, border box = 200px and content = 200 − 20 − 4 = 176px.

Trap Margin never enters declared border-box width; it remains outside.

16 · HTML + Form Build Order W2 · W5 · SECTION C

1. Doctype, html, head/title, body, one h1.
2. Form action + method; labels/controls with matching for/id and name.
3. Correct types; radios share name; submit control.
4. One JS validation hook with return.
5. Close non-void elements; validate generated HTML.

17 · Worked 2: DOM Read CH8 WORKED EXAMPLE

Given: form named order, text box named and identified as qty.

document.order.qty.value
document.getElementById("qty").value

Answer: both read the same value and start from document under window. The second route reaches any element with that unique id.

Trap getElementById is case-sensitive; final d is lower-case.

18 · JavaScript Long Answer PRACTICE PAPER

<script>
function total(){
 var p=document.getElementById("price").value;
 var q=document.getElementById("quantity").value;
 if(p===""||q===""){
  alert("Complete both fields");return false;
 }
 alert(Number(p)*Number(q));
 return true;
}
</script>

Use either onsubmit="return total();" or button onclick, not both. Client validation can be bypassed.

19b · XML→PHP→HTML Drill W7

20 · Worked 3: CRC CH10 WORKED EXAMPLE

Given: message 110101; generator x³ + 1 = 1001.

1. Generator has 4 bits; append 3 zeros: 110101000.
2. XOR: 010001000 → 000011000 → 000001010 → 000000011.
3. Remainder 011; transmit 110101011.
4. Receiver divides by 1001 and gets 000: no error detected.

Self-check Remainder width k−1 = 3. Zero detects no error; it does not prove correctness.

21 · Error/Compression Traps W10

Parity: one flip changes parity; two can preserve it. Run length: good for runs, poor for alternating data. Dictionary: replaces repeated phrases. Lossy media trades detail for size.

22 · CRC/Huffman Chooser W10

23 · Worked 4: Huffman COURSE WORKED EXAMPLE

Encode: coffeetoffee (12 characters).

1. Counts: f 4, e 4, o 2, c 1, t 1; total 12.
2. Merge c+t→2; o+2→4; e+4→8; f+8→12.
3. Codes: f 0; e 10; o 110; c 1110; t 1111.
4. Message: 11101100010101111110001010 = 26 bits.
5. Original 12×8=96. Saving 1−26/96=70/96≈72.9%. Original:compressed=96:26=48:13.

bit check = 4×1 + 4×2 + 2×3 + 1×4 + 1×4 = 26

Trap Ties may change codes, not total. Show merges so the tree is traceable.

24 · Decode / Verify W10

Build + decode

Prefix-free: no code begins another, so symbol endings need no separators. A violation means the tree was read wrongly.

Ties: several valid trees may result. Record merge order; verify length by frequency×depth and direct bit count.

25 · Worked 5: Key Choice CH11 WORKED EXAMPLE

1. Only Alice reads Bob’s contract: Bob encrypts with Alice’s public key.
2. Only Alice holds Alice’s private key, so only she decrypts.
3. Alice proves reply: hash, sign digest with Alice’s private key.
4. Bob verifies with Alice’s public key and compares his digest: match supports origin + integrity.

Counterfeit key: attacker replaces a directory key, reads, re-encrypts with genuine key and forwards. A certificate authority signature binds identity to public key; verify chain and validity period.

26 · Attack/Defence Drill W12 METHOD

A virus copies into files and needs its host run; a worm spreads unaided. Phishing deceives a person; pharming alters DNS so a genuine address reaches a spoofed site. Not all malware is a virus.

Privacy: cookies are text, not code, but enable tracking. Opt-in requires agreement first; opt-out collects until refused.

27 · One-Minute Error Scan ALL WEEKS

• Routing ≠ forwarding; Web ≠ Internet.
• XML valid includes DTD; HTML meaning before appearance.
• ID specificity before classes; margin outside width.
• GET visible in URL; POST not automatically encrypted.
• XPath starts 1; PHP array starts 0.
• JS + joins; PHP . joins; cast values.
• CRC width = generator bits − 1.