Database Systems Design, Implementation, and Manageme.docx

Database Systems:
Design, Implementation, and Management
Ninth Edition
Chapter 4
Entity Relationship (ER) Modeling
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Database Systems, 9th Edition
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ObjectivesIn this chapter, students will learn:The main
characteristics of entity relationship componentsHow
relationships between entities are defined, refined, and
incorporated into the database design processHow ERD
components affect database design and implementation
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The Entity Relationship Model (ERM)ER model forms the basis
of an ER diagramERD represents conceptual database as viewed
by end userERDs depict database’s main
components:EntitiesAttributesRelationships
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EntitiesRefers to entity set and not to single entity
occurrenceCorresponds to table and not to row in relational
environmentIn Chen and Crow’s Foot models, entity is
represented by rectangle with entity’s nameEntity name, a noun,
written in capital letters
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AttributesCharacteristics of entitiesChen notation: attributes
represented by ovals connected to entity rectangle with a
lineEach oval contains the name of attribute it representsCrow’s
Foot notation: attributes written in attribute box below entity
rectangle

*
*
Attributes (cont’d.)Required attribute: must have a
valueOptional attribute: may be left emptyDomain: set of
possible values for an attributeAttributes may share a
domainIdentifiers: one or more attributes that uniquely identify
each entity instanceComposite identifier: primary key composed
of more than one attribute
*

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Attributes (cont’d.)Composite attribute can be
subdividedSimple attribute cannot be subdividedSingle-value
attribute can have only a single valueMultivalued attributes can
have many values
*
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Attributes (cont’d.)M:N relationships and multivalued attributes
should not be implementedCreate several new attributes for
each of the original multivalued attributes’ componentsCreate
new entity composed of original multivalued attributes’
componentsDerived attribute: value may be calculated from
other attributesNeed not be physically stored within database

*
*
RelationshipsAssociation between entitiesParticipants are
entities that participate in a relationshipRelationships between
entities always operate in both directionsRelationship can be
classified as 1:MRelationship classification is difficult to
establish if only one side of the relationship is known
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Connectivity and CardinalityConnectivity Describes the
relationship classificationCardinality Expresses minimum and
maximum number of entity occurrences associated with one
occurrence of related entityEstablished by very concise
statements known as business rules

*
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Existence DependenceExistence dependenceEntity exists in
database only when it is associated with another related entity
occurrenceExistence independenceEntity can exist apart from
one or more related entitiesSometimes such an entity is referred
to as a strong or regular entity
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Relationship StrengthWeak (non-identifying)
relationshipsExists if PK of related entity does not contain PK
component of parent entityStrong (identifying)
relationshipsExists when PK of related entity contains PK
component of parent entity

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Fig 4.8 shows how the Crow’s Foot notation depicts a week
relationship by placing a dashed relationship line between the
entities. The tables shown below the ERD illustrate how such a
relationship is implemented.
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Figure 4.9 depicts the strong (identifying) relationship with a
solid line between the entities. Whether the relationship
between COURSE and CLASS is strong or weak depends on
how the CLASS entity primary key is defined.
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Weak EntitiesWeak entity meets two conditionsExistence-
dependentPrimary key partially or totally derived from parent
entity in relationshipDatabase designer determines whether an
entity is weak based on business rules

*
*
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Relationship ParticipationOptional participationOne entity
occurrence does not require corresponding entity occurrence in
particular relationshipMandatory participationOne entity
occurrence requires corresponding entity occurrence in
particular relationship

*
*
The different scenarios are a function of the semantics of the
problem; that is, they depend on how the relationship is defined.
CLASS is optional. It is possible for the department to create
the entity COURSE first and then create the CLASS entity after
making the teaching assignments. In the real world, such a
scenario is very likely; there may be courses for which sections
(classes) have not yet been defined. In fact, some courses are
taught only once a year and do not generate classes each
semester.
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CLASS is mandatory. This condition is created by the constraint
that is imposed by the semantics of the statement "Each
COURSE generates one or more CLASSes." In ER terms, each
COURSE in the "generates" relationship must have at least one

CLASS. Therefore, a CLASS must be created as the COURSE is
created, in order to comply with the semantics of the problem.
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Associative (Composite) EntitiesAlso known as bridge
entitiesUsed to implement M:N relationshipsComposed of
primary keys of each of the entities to be connectedMay also
contain additional attributes that play no role in connective
process
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*
A class may exist (at least at the start of registration) even

though it contains no students. Therefore, if you examine Figure
4.24, an optional symbol should appear on the STUDENT side
of the M:N relationship between STUDENT and CLASS.
You might argue ta that to be classified as a STUDENT, a
person must be enrolled in at least one CLASS.
Therefore, CLASS is mandatory to 0 STUDENT from a purely
conceptual point of view. However, when a student is admitted
to college, that student has not (yet) signed up for any classes.
Therefore, at least initially, CLASS is optional to
STUDENT.
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Because the M:N relationship between STUDENT and CLASS is
decomposed into two 1:M relationships
through ENROLL, the optionalities must be transferred to
ENROLL. (See Figure 4.25.) In other words, it now becomes
possible for a class not to occur in ENROLL if no student has as
signed up for that class. Because a class need not occur in
ENROLL, the ENROLL entity becomes optional to CLASS. And
because the ENROLL entity is created before any students have
signed up for a class, the ENROLL entity is also optional to
STUDENT, at least initially.

*
Developing an ER DiagramDatabase design is an iterative
processCreate detailed narrative of organization’s description
of operationsIdentify business rules based on description of
operationsIdentify main entities and relationships from business
rulesDevelop initial ERDIdentify attributes and primary keys
that adequately describe entitiesRevise and review ERD
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Tiny college is divided into several schools: business, arts and
sciences, education, and applied sciences. Each school is
administered by a dean who is a professor. Each professor can
be the dean of only one school, and a professor is not required
to be the dean of any school. Therefore, a 1:1 relationship exists
between professor ands school.
Note that the cardinality can be expressed by writing (1,1) next
to the entity PROFESSOR and (0,1) next to the entity SCHOOL.
Each school comprises several departments. Note again the
cardinality rules: The smallest number of departments operated
by a school is one, and the largest number of department is
indeterminate (N). On the other hand, each department belongs
to only a single school; thus, the cardinality is expressed by
(1,1).

*
Each department may offer courses. Tiny college had some
departments that were classified as “research only”. Those
departments would not offer courses. Therefore, the course
entity would be optional to the department entity.
*
1:M relationship exists between COURSE and CLASS.
However, because a course may exist in Tiny College's course
catalog even when it is not offered as a class in a current class
schedule, CLASS is
optional to COURSE. Therefore, the relationship between
COURSE and CLASS looks like Figure 4.28.
*
Each department should have one or more professors assigned
to it. One and only one of those professors chairs the
department, and no professor is required to accept the chair
position. Therefore, DEPARTMENT is optional to PROFESSOR

in the "chairs" relationship. Those relationships are summarized
in the ER segment shown in Figure 4.29.
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Each professor may teach up to four classes; each class is a
section of a course. A professor may also be on a research
contract and teach no classes at all. The ERD segment in Figure
4.30 depicts those conditions.
*
This M:N relationship must be divided into two 1:M
relationships through the use of the ENROLL entity, shown in
the ERD segment in Figure 4.31. But note that the optional
symbol is shown next to ENROLL. If a class exists but has no
students enrolled in it, that class doesn't occur in the ENROLL
table. Note also that the ENROLL entity is weak: it is
existence-dependent, and its (composite) PK is composed of the
PKs of the STUDENT and CLASS entities. You can add the
cardinalities (0,6) and (0,35) next to the ENROLL entity to
reflect the business rule constraints, as shown in Figure 4.31.

*
Each department has several (or many) students whose major is
offered by that department. However, each student has only a
single major and is, therefore, associated with a single
department. (See Figure 4.32.) However, in the Tiny College
environment, it is possible—at least for a while—for a student
not to declare a major field of study. Such a student would not
be associated with a department; therefore, DEPARTMENT is
optional to STUDENT. It is worth repeating that the
relationships between entities and the entities themselves reflect
the organization's operating environment. That is, the business
rules define the ERD components.
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Each student has an advisor in his or her department; each
advisor counsels several students. An advisor is also a
professor, but not all professors advise students. Therefore,
STUDENT is optional to PROFESSOR in the "PROFESSOR
advises STUDENT" relationship. (See Figure 4.33.)

*
As you can see in Figure 4.34, the CLASS entity contains a
ROOM_CODE attribute. Given the naming conventions, it is
clear that ROOM_CODE is an FK to another entity. Clearly,
because a class is taught in a room, it is reasonable to assume
that the ROOM_CODE in CLASS is the FK to an entity named
ROOM. In turn, each room is located in a building. So the last
Tiny College ERD is created by observing that a BUILDING
can contain many ROOMs, but each ROOM is found in a single
BUILDING. In this ERD segment, it is clear that some buildings
do not contain (class) rooms. For example, a storage building
might not contain any named at all.
*
*

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Database Design Challenges:
Conflicting GoalsDatabase designers must make design
compromisesConflicting goals: design standards, processing
speed, information requirementsImportant to meet logical
requirements and design conventionsDesign is of little value
unless it delivers all specified query and reporting
requirementsSome design and implementation problems do not
yield “clean” solutions
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SummaryEntity relationship (ER) model Uses ERD to represent
conceptual database as viewed by end userERM’s main
components:EntitiesRelationshipsAttributesIncludes
connectivity and cardinality notations

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Summary (cont’d.)Connectivities and cardinalities are based on
business rulesM:N relationship is valid at conceptual levelMust
be mapped to a set of 1:M relationships
A pdf has been placed on Moodle with selections from Jewish
Scriptures and other writings. Read Psalm 137, which appears
on the 12th page of this pdf, p. 364 of the text reproduced there.
Explain the historical and spiritual context of this text. In
particular, explain why singing a song of Zion in an alien land
an issue for the Jewish author of this text. And if it’s not the
place where they are that is the issue, why can’t Jews just sing
some other song? What’s so important to them about singing
what is here called “a song of the Lord?” Be as specific as
possible in sketching in the background of sorrow expressed
here.
2 pages, typed and double-spaced.
Due Tuesday January 27th.
first paper topic
Strategies for writing short papers
Good Strategies
Trust your own ability to read and interpret the text.
Read the text carefully, and make use of relevant sections of the
textbook to help make sense of the context in which the text you

are considering appears.
Put your explanation in your own words. Think of how you
might explain what you’ve learned to a friend who asked you
about the class you’re taking.
Bad Strategies
Quoting the powerpoint slides used in class.
Going online to find how others have interpreted this text.
Plagiarizing online sources.
Forgetting to provide the explanation asked for in the
assignment.
Optional readings on Moodle
The pdf of readings on Moodle includes a selection from Philo
of Alexandria (pp. 15 – 16 of the pdf); examples drawn from
Mishnah and Talmud are on pp. 19 – 21; Maimonides’ Thirteen
Principles are on p. 22. This is followed by selections from the
Kabalistic text Zohar.
Shema: The Daily Prayer of Judaism
Hear, Israel, the Lord is our God, the Lord is One.
Blessed be the Name of His glorious kingdom for ever and ever
And you shall love the Lord your God with all your heart and
with all your soul and with all your might.
And these words that I command you today shall be in your
heart.
And you shall teach them diligently to your children, and you
shall speak of them

when you sit at home, and when you walk along the way, and
when you lie down and when you rise up.
And you shall bind them as a sign on your hand, and they shall
be for frontlets between your eyes.
And you shall write them on the doorposts of your house and on
your gates. [Deut. 6:4-9]
And it shall come to pass if you surely listen to the
commandments
that I command you today, to love the Lord your God,
and to serve him with all your heart and all your soul,
That I will give rain to your land, the early and the late rains,
that you may gather in your grain, your wine and your oil.
And I will give grass in your fields for your cattle and you will
eat and you will be satisfied.
Beware, lest your heart be deceived,
and you turn and serve other gods, and worship them.
And anger of the Lord will blaze against you, and he will close
the heavens and there will not be rain,
and the earth will not give you its fullness,
and you will perish quickly from the good land that the Lord
gives you.
So you shall put these, my words, on your heart and on your
soul;
and you shall bind them for signs on your hands, and they shall
be for frontlets between your eyes.

And you shall teach them to your children, and you shall speak
of them
when you sit in your house, and when you walk on the way, and
when you lie down, and when you rise up.
And you shall write them on the doorposts of your house and on
your gates.
In order to prolong your days and the days of your children on
the land that the Lord promised
your fathers that he would give them, as long as the days that
the heavens are over the earth. [Deut. 11: 13-21]
And the Lord spoke to Moses, saying...
And they shall be tzitzit for you, and when you look at them
you will remember all of the Lord's commandments
and do them and not follow after your heart
and after your eyes, which lead you astray.
In order to remember and do all My commandments, and be
holy for your God.
I am the Lord, your God, who led you from the land of Egypt
to be a god to you. I am the Lord, your God. [Numbers
15: 37-41]
Prayer: “Tefilah”Prayer reminds us of G*d’s presence in our
lives and our relationship to Him.Prayer requires a special kind
of concentration known as kavanah, which involves an
intensifying of our awareness of G*dPrayers are most
commonly said in a group, known as a minyan; this “quorum”
requires at least 10 adult Jewish men.

Tefillin
These are leather boxes worn on the forehead and strapped to
the upper arm during daily recital of shema.
Also known as phylacteries, they contain written copies of the
shema which guard against the temptation of sin.
Preparing for prayer, with tefillin on head and arms and wearing
Tallit shawl.
Mezuzah (plural: Mezuzot)These are small scroll cases mounted
on the doorposts of Jewish homes.The name “mezuzah” applies
to both the scroll and the case which holds it.The scroll contains
part of the text of the shema, and it should be hand-written, not
mechanically made.A dedication ceremony is held when the
mezuzah is installed on the house, and the mezuzah should be
removed when the family moves away so that nothing
disrespectful may be done to the scroll.
Outward signs of Judaism
Circumcision of males.
Tallit and Tzitzit: The tallit is a shawl worn during prayer;
tzitzit are the fringes tied onto the corners of this shawl. The
tying of fringes onto four-cornered garments is specified in the
Torah as a reminder of the mitzvot. (This is also part of the
Shema)
Yarmulke: a small cap, also worn during prayer.

Differing views of scriptures
The traditional Jewish view is that Moses wrote the Torah after
receiving its contents as a revelation on Mt. Sinai.
Modern scholarship holds that the text of Torah is a redaction, a
reconstruction done after the return from Babylon which united
several strands of literature into one document. This view is
known as the documentary hypothesis (see p. 94 of Religions of
the West Today for a more detailed account of this viewpoint).
Judaism in a Hellenic worldAs a result of the Diaspora, Jews
found themselves scattered across the Hellenized Mediterranean
world.Ideas drawn from Greek philosophy, mathematics, and
science dominated this era. The application of reason (logos) as
part of a systematic investigation of nature was the ruling
principle, while the guidance provided by prophetic revelation
was seen as limited in scope. Given the differences between
Hellenic and Judaic cultures, questions of how to maintain
Jewish identity outside of the traditional homeland became more
pressing and difficult to answer. Some Jews became
assimilated to the wider culture, while others formed isolated
Jewish communities, such as the Essenes. Intellectually,
allegorical interpretation was developed as a means of
integrating Judaism with Greek philosophy; this is a method of
reading texts symbolically. Philo of Alexandria is a good
example of a Jewish thinker who engages in this kind of reading
of the traditional scriptures.
Apocalyptic Judaism“Apocalypse” is a Greek word meaning
“unconcealed” or “out of hiding.”In the centuries following the
return from exile, as Jewish communities came into contact with
other cultures to a greater extent than before, some Jews
withdrew into isolated communities. In these communities, the

idea that God’s plan for the world was still in place (and hence
yet to be revealed) led to a variety of apocalyptic traditions.It
was in this context that the traditions surrounding the coming of
the Moshiach developed.
Moshiach: the anointed oneThe Moshiach (or Mashiah) will be
both a spiritual and a secular ruler, a human appearing in the
end times. Jewish eschatology holds that this will inaugurate
“The World To Come,” not an afterlife but rather a period of
peace and prosperity for the world. He will restore the temple
in Jerusalem.He will be of the line of David.He will be a great
military leader, and also a judge who establishes Jewish Law.In
every generation, the potential exists for the Moshiach to arise,
should conditions on Earth call for it (either great sinfulness or
great goodness).Christians believe that Jesus was the Moshiach,
but Jews do not accept this claim, believing instead that The
World To Come still lies in the future.
The “Dual Torah”
Jews believe that in addition to the written Torah handed to
Moses at Sinai, there was an oral tradition also transmitted at
Sinai but never written down until after the destruction of the
second temple. This oral tradition became the Mishnah. Not all
movements of Judaism accept this tradition, as some movements
focus simply on the traditional written Torah.
More Texts of JudaismMishnah: written down around 200 c.e.,
these are rabbinical commentaries on the Torah (also believed
to be the oral Torah).Gemara: These texts are completed
between 400 and 600 c.e. by Jewish communities in Jerusalem

and Babylonia (there are two distinct collections of
commentary). These are Rabbinical commentaries on the
Mishnah. Talmud: Talmud comprises both Mishnah and Gemara.
The Talmudic tradition of commentary and interpretation
continues to this day. While it is mainly a scholarly tradition,
the idea that continual discussion and debate over the meaning
of scriptural texts is at the heart of Jewish experience for
anyone who identifies as a Jew. Midrash: these “investigations”
are commentaries written by Rabbis in the early centuries of the
common era. Midrash has come to be a general term for any
commentary on scripture intended to provide advice for Jews
seeking guidance in life.
Halakhah: Jewish Law
“the path that one walks.”Mitzvot: commandments from the
Torah.Gezirah: (“a fence around the Torah”) laws instituted by
Rabbis to help uphold the Mitzvot (e.g., a requirement to not
even handle implements of work on Shabbat, things like pencils,
calculators, etc.).Takkanah: laws instituted by Rabbis, but with
no special reference to the Torah (e.g., the requirement to light
candles on Hanukkah).Minhag: customs which have been
recognized as having the status of law (e.g., extending the
observance of holidays to a second day so that the astronomical
timing of the day will not be interfered with).
Rabbinical JudaismThe age of cogency (640 – 1800 c.e.) saw a
growth in the power of Rabbis (teachers) within the Jewish
community. Rabbis are authorities on Halakhah, and they
advise Jews on difficult questions of legal and moral
interpretation.It is the Rabbis who develop and maintain the
Mishnah and Talmud, systematizing the substance of Jewish

belief.The 13 principles of faith developed by Moses Ben
Maimon (Maimonides) is an emblematic statement of Rabbinical
authority.
Officials of the Jewish Community
Kohein: a priest who is charged with the duty of carrying out
sacrifice in the Temple; traditionally identified as descendants
of Aaron. (Levites were also charged with special duties
pertaining to the maintenance of the temple.)
Rabbi: a teacher; someone well-versed in halakah; Rabbis are
not necessarily kohein and so do not perform any sacrificial
rituals.
Chazzan: a cantor who leads the group attending synagogue in
singing and prayers.
Synagogue:
The House of Assembly and PrayerSynagogue is the term used
by Conservative Jews to refer to the place of worship; this word
literally means “house of assembly” (Hebrew: beit
k’nesset).Reform Jews call it a temple, since they believe that
the ancient temple is remade wherever and whenever they
gather.Orthodox Jews call it a Shul (derived from the German
word for school; a place of learning).
The synagogue is the center of the Jewish community, and it
serves asThe place of worship or prayerThe place for rituals,
such as the Bar MitzvahA place for social gatherings

A Torah Scroll
Every Synagogue has a Torah scroll (called a Sefer Torah), kept
in an Ark (Hebrew: aron kodesh, or holy cabinet). This Ark has
both a curtain and doors, which are opened and closed as part of
worship services. The ark usually faces Jerusalem. In front of
this is an oil lamp, satisfying the mitzvah to keep a light
burning outside the Ark. A bimah (altar) is placed in front of
the Ark, and the scroll is placed here to be read from during
services.
In Orthodox synagogues, women are separated from men,
sometimes by a curtain or a wall. (This is meant to minimize
distraction for the men while they are praying.)
Aron Kodesh Torah Scroll on Bimah

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